UNIVERSITY  OF   CALIFORNIA    PUBLICATIONS. 

COLLEGE  OF  AGRICULTURE. 

AGRICULTURAL  EXPERIMENT  STATION, 

BERKELEY,  ( JA  LIFORNIA. 


THE  GRAPE  LEAF-HOPPER. 

By  H.  J.  QUAYLE. 


BULLETIN     No.     198. 

(Berkeley,  Cal.,  July,  1908.) 


SACRAMENTO: 
w.  Wj  shannon,     :     :     :     :     superintendent  state  printing 

1908. 


BENJAMIN  IDE  WHEELER,  Ph.D.,  LL.D.,  President  of  the  University. 


EXPERIMENT  STATION  STAFF. 

E.  J.   WICKSON,  M.A.,  Director  and  Horticulturist. 

E.  W.  HILGARD,  Ph.D.,  LL.D.,  Chemist. 

W.  A.  SETCHELL,  Ph.D.,  Botanist. 

EL  WOOD  MEAD,  M.S.,  C.E.,  Irrigation  Engineer.      (Absent  on  leave.) 

LEROY  ANDERSON,  Ph.D.,  Dairy  Industry  and  Superintendent  University  Farm. 

M.  E.  JAFFA,  M.S.,  Nutrition  Expert,  in  charge  of  the  Poultry  Station. 

C.  W.  WOOD  WORTH,  M.S.,  Entomologist. 

R.  H.  LOUGHRIDGE,  Ph.D.,  Soil  Chemist  and  Physicist. 

G.  W.  SHAW,  M.A.,  Ph.D.,  Agricultural  Technologist,  in  charge  of  Cereal  Stations. 

GEORGE  E.  COLBY,  M.S.,   Chemist,  in  charge  of  Agricultural  Chemical  Laboratory. 

RALPH  E.  SMITH,  B.S.,  Plant  Pathologist  and  Superintendent  of  Southern  California 

Pathological  Laboratory  and  Experiment  Station.      Whittier. 
A.   R.   WARD,   B.S.A.,   D.V.M.,   Veterinarian  and  Bacteriologist. 

E.  W.  MAJOR,  B.Agr.,  Animal  Industry. 
H.  M.  HALL,  M.S.,  Assistant  Botanist. 

H.  J.  QUAYLE,  A.B.,  Assistant  Entomologist.     Whittier. 

W.    T.    CLARKE,    B.S.,    Assistant   Horticulturist    and    Superintendent    of    University 

Extension  in  Agriculture. 
JOHN  S.  BURD,  B.S.,  Chemist,  in  charge  of  Fertilizer  Control. 
C.  M.  HARING,  D.V.M.,  Assistant  Veterinarian  and  Bacteriologist. 
H.  A.  HOPPER,  B.S.A.,  Assistant  in  Dairy  Husbandry. 
J.  H.  NORTON,  M.S.,  Assistant  Chemist  in  charge  Fertilizer)      „ 

Experiments,  I      Citrus  Experiment 

T.  F.  HUNT,  B.S.,  Assistant  Horticulturist,  )  Station,  Riverside. 

E.  B.  BABCOCK,  B.S.,  Assistant  Plant  Pathologist. 

E.  H.  SMITH,  M.S.,  Assistant  Plant  Pathologist. 

F.  L.  YEAW,  B.S.,  Assistant  Plant  Pathologist. 

H.  J.  RAMSEY,  M.S.,  Assistant  Plant  Pathologist, )        Southern  California  Patholog- 

C.  O.  SMITH,  M.S.,  "  "  "  )  ical  Laboratory,  Whittier. 
R.  E.  MANSELL,  Assistant  in  Horticulture,  in  charge  of  Central  Station  Grounds. 
RALPH  BENTON,  B.S.,  B.L.,  Assistant  in  Entomology  (Apiculture) . 

A.  J.  GAUMNITZ,  M.S.,  Assistant  in  Cereal  Investigations. 

RACHAEL  CORR,  M.A.,  Assistant  in  Cereal  Laboratory. 

HANS  C.  HOLM,  B.S.,  Assistant  in  Zymology. 

P.  L.  McCREARY,  B.S.,  Laboratory  Assistant  in  Fertilizer  Control. 

F.  E.  JOHNSON,  B.  L.,  Assistant  in  Soil  Laboratory. 

M.  E.  STOVER,  B.S.,  Assistant  in  Agricultural  Chemical  Laboratory. 

D.  R.  HOAGLAND,  A.B.,  Assistant  in  Agricultural  Chemical  Laboratory. 
CHARLES  FUCHS,  Curator  Entomological  Museum. 

P.  L.  HIBBARD,  B.S.,  Assistant  Fertilizer  Control  Laboratory. 

M.  E.  SHERWIN,  Field  Assistant  in  Agronomy. 

W.  H.  VOLCK,  Field  Assistant  in  Entomology.     Watsonville. 

E.  L.  MORRIS,  B.S.,  Field  Assistant  in  Entomology.     San  Jose. 
J.  S.  HUNTER,  Field  Assistant  in  Entomology.     San  Mateo. 

D.  L.  BUNNELL,  Clerk  to  the  Director. 


JOHN  TUOHY,  Patron,  J  Tulare  Suhstation)  Tulare. 

J.  T.  BEARSS,  Foreman,       ) 


J.  W.  ROPER,  Patron,  ) 

E.  C.  MILLER,  In  charge,    ) 
ROY  JONES,  Patron,  ) 

N.  D.  INGHAM,  Foreman,    j 
VINCENT     J.     HUNTLEY,     Foreman     of     California    Poultry     Experiment     Station, 
Petaluma. 


University  Forestry  Station,  Chico. 
University  Forestry  Station,  Santa  Monica. 


The  Station  publications  (Reports  and  Bulletins),  so  long  as  avail- 
able, will  be  sent  to  any  citizen  of  the  State  on  application. 


OUTLINE. 


Page. 
GENERAL   CONSIDERATIONS    177 

Early   accounts ;   Destructiveness ;   Distribution,  general,   local. 

LIFE  HISTORY  AND  HABITS 181 

Overwintering  Adults    181 

Food  habits ;  Relation  of  food  to  development  and  activity ;  Influence  of 
temperature  upon  activity ;  Proportion  of  the  sexes ;  Migrations ;  Time  they 
attack  the  vine  ;  Do  they  feed  exclusively  on  the  vine ;  Habits  on  the  vine ; 
Copulation  and  oviposition. 

The  Egg * 186 

Description  and  appearance ;  Wnere  laid ;  Number ;  Rate  of  egg  laying ; 
Incubation  period ;  Percentage  of  eggs  that  hatch ;  Effect  of  oviposition 
upon  the  leaf. 

The  Nymph  192 

The  hatching  process ;  First  stage ;  Second  stage ;  Third  stage ;  Fourth 
stage ;  Fifth  stage ;  Moulting ;  Habits  of  feeding ;  Transfer  to  other  food 
plants. 

The  Adult  196 

Time  of  reaching  maturity ;  Feeding  habits ;  Copulation  and  oviposition ; 
Activity  and  migrations ;  Activity  of  the  sexes ;  Proportion  of  the  sexes ; 
Differences  in  coloring ;  The  varieties  of  the  species  comes  ;  Proportion  of  the 
varieties ;  Common  name  of  the  insect ;  Preferences  for  different  varieties  of 
vines. 

Development    200 

Length  of  life  cycles ;  Number  of  generations  ;  Comparisons  of  development 
in  other  localities. 

NATURAL  CONTROL   202 

Climatic  ;  Parasitic  ;  Predatory  ;  Fungous. 

MECHANICAL   CONTROL    203 

Blowers  and  suction  ;  Torches ;  Dry  powders  ;  Sticky  shields  ;  Fumigation  ; 
Sprays  and  washes ;  Screens  or  cages. 

FARM  PRACTICES    214 

Plowing ;  Sheeping. 

SUMMARY    215 

LITERATURE    217 


THE  GRAPE  LEAF-HOPPER 

(Typhlocyba  comes  Say.) 
By  H.  J.   QUAYLE. 


GENERAL   CONSIDERATIONS. 

Early  Accounts. — The    grape    leaf-hopper    was    first    named    and 
described  by  Thomas  Say1  in  the  year  1825.     Specimens  were  taken 


Fig.    1.     Grape  leaf' showing  first  indication  of  injury  due  to  hoppers.      The 
white    specks    represent    where    the    insects    have    been    feeding. 

that  year  from  Missouri,  and  three  or  four  years  later  it  was  reported 
as  an  important  pest  of  the  vine  in  Massachusetts.  Harris2  in  1841 
wrote  the  first  complete  account  of  the  insect  and  fully  appreciated 

1  Jour.  Acad,  of  Nat.  Sciences.  Phil.  iv.  327. 

2  Harris.  Ins.  Inj.  to  Vegetation,  Flint  Ed.,  227. 


178 


UNIVERSITY   OF   CALIFORNIA EXPERIMENT   STATION. 


the  injury  caused  by  it,  and  ever  since  that  time  it  has  occupied  a 
very  important  place  in  the  literature  of  grape  insects  in  this  country. 
Harris's  account  of  the  insect  remained  the  standard  for  a  long 
while,  and  no  very  thorough  work  was  done  on  the  life  history  of 
the  insect  until  it  was  undertaken  by  Slingerland  in  1901.1 

In  California  it  has  been  reported  as  a  pest  of  the  vine  since  1875. 
The  accounts  of  insects  in  the  "Pacific  Rural  Press"  furnish  a 
fairly  good  index  on  the  occurrence  of  injurious  species  in  this 
State,  and  the  first  account  there  given  is  in  the  issue  of  April  12, 
1879.     Notices   regarding  this   insect   have   appeared   frequently   in 


Fig.  2.  Young  grape  leaves  in  advanced  stage  of  hopper  injury.  These  leaves  had 
completely  dried  up  and  fallen  to  the  ground  in  the  early  spring.  Photographed 
April    20,    1907. 

the  press  of  the  State,  as  well  as  other  publications,  since  that  time. 
Brief  notices  of  its  occurrence  have  been  printed  in  the  State  Horti- 
cultural Commission  reports,  and  a  bulletin  on  the  insect  was  issued 
from  this  station  in  1897. 2 

Destructiveness. — With  the  exception  of  the  phylloxera,  the  vine 
hopper  is  undoubtedly  the  most  destructive  insect  pest  of  the  vine 
in  the  State.     It  is  more  uniformly  present  than  any  other  insect 

1  Slingerland,  Cornell  Exp.  Sta.  Bull.  215, 
•Woodworth,  Cal.  Agr.  Exp.  Sia.  Bull.  116. 


Bulletin  198. 


THE  GRAPE  LEAF-HOPPER. 


179 


attacking  the  vine,  and  each  year  in  some  parts  of  the  State  it 
occurs  in  very  great  numbers,  and  in  such  sections,  it  levies  a  heavy 
tax  upon  the  vineyard  interests.  To  give  expression  to  this  loss  in 
money  value,  for  example,  in  one  vineyard  of  about  a  thousand 
acres  near  Madera,  the  owner  estimated  that  the  damage  done  last 
year  by  hoppers  would  aggregate  about  $10,000. 

The  grape  leaf-hopper  belongs  to  the  class  of  injurious  insects 
that  obtain  their  food  by  sucking  the  juices  from  the  plant.  Scale 
insects  and  plant  lice  are  other  well  known  pests  belonging  to  this 
same  general  group,  which  obtain  their  food  in  much  the  same  way 
that  the  mosquito  sucks  our  blood.  The  sharp  pointed  beak  or 
proboscis  of  the  hopper  (Fig.  4)  is  thrust  into  the  tissues  of  the 
grape  leaf  and  the 
liquid  parts  extract- 
ed therefrom.  The 
feeding  is  done 
mostly  on  the  un- 
derside of  the  leaf, 
and  those  leaves 
around  the  base  of 
the  vine  are  the 
ones   first   attacked. 

The  first  indica- 
tion of  their  work 
is  a  mottled  appear- 
ance of  the  leaf  due 
to  the  pale  spots 
formed  wherever  the 
beak  has  been  in- 
serted and  the  green  parts  taken  out  (Fig.  1).  As  the  feeding  continues 
these  spots  become  more  numerous,  and  this  pale  yellow  color 
spreads  over  the  entire  surface;  and  finally  the  leaf  turns  brown 
and  drops  off  (Fig.  2).  This  injury  has  been  observed  as  early 
as  April  or  May,  and  thus  the  vine  from  the  very  beginning 
of  the  season  is  prevented  from  making  its  normal  growth.  As 
the  hoppers  increase  in  numbers  the  injury  increases  with  the 
advancement  of  the  season.  In  midsummer  quite  a  large  area 
about  the  crown  of  the  vine  will  show  all  the  leaves  pale  colored  or 
completely  dried  up,  and,  in  severe  cases,  the  entire  vine  is  thus 
affected.  This  drying  up  and  dropping  off  of  the  leaves  allows  the 
sun  to  have  free  access  to  the  fruit  and  may  cause  sunburn.  We  have 
seen  the  fruit  thus  exposed  and  badly  sunburned  as  early  as  the 
middle  of  June.     The  falling  off  of  the  leaves  prematurely  also  pre- 


Fig.  3.  The  foliage  and  fruit  of  the  grape  is  often  badly- 
smutted  by  the  excrement  of  hoppers.  The  black 
specks   on   the   above   leaf   indicate   this. 


180 


UNIVERSITY   OF   CALIFORNIA EXPERIMENT   STATION. 


labium 


vents  the  berry  from  maturing  properly  since  it  is  in  the  leaves  of 
the  plant  that  the  sugar  of  the  berry  is  manufactured.  The  grape 
thus  loses  much  of  its  flavor  and  sweetness,  and  likewise  the  char- 
acteristic coloring,  which  is  so  desirable  in  certain  table  varieties,  is 
not  attained.  The  fruit,  furthermore,  is  badly  smutted  by  the  exuda- 
tions of  the  insects,  and  this  serves  as  a  harboring  place  for  the 
collection  of  dust  and  dirt,  and  for  the  growth  of  fungi   (Fig.  3). 

The  dropping  of  the  leaves  or  any 
interference  with  their  normal  func- 
tions likewise  has  its  effect  on  the 
growth  of  the  wood  of  the  vine.  The 
canes  fail  to  ripen  normally  for  the 
next  year's  wood,  and  many  of  the 
buds  fail  to  develop  in  the  following 
spring.  The  vine  may  thus  be  more 
or  less  permanently  stunted  in  growth, 
and  even  killed  in  severe  cases  of 
Wan  dibits    grape  leaf -hopper  injury. 

Distribution;  General. — The  grape 
leaf -hopper  {Typhlocyba  comes  Say) 
is  a  widely  distributed  native  Ameri- 
can insect  occurring  in  the  United 
States  practically  wherever  the  vine  is 
grown.  It  is  frequently  notably  in- 
jurious in  the  grape  belts  of  New 
York  and  Ohio,  as  well  as  other  less 
important  grape  sections  in  this 
country.  In  Europe  this  species  is 
replaced  by  two  other  related  species, 
Typhlocyba  flavescens  and  Typhlocyba 
viticola.  The  former  seems  to  be  the 
more  injurious  of  the  two  and  occurs 
throughout  all  of  temperate  Europe 

and   northern    Africa,   while   the   latter   is   confined   mostly   to   Italy 

and   the   neighboring   islands.1 

Local. — In  California  our  species  is  found  in  practically  all  of  the 
vine  growing  sections,  but  is  most  injurious  in  the  Sacramento  and 
San  Joaquin  valleys.  In  the  coast  valleys  another  larger  species 
(Tettegonia  atropunctata)  is  frequently  injurious,  most  commonly 
during  the  earlier  part  of  the  season.  This  species  appears  not  to 
feed  exclusively   on   the   vine,   and   during   midsummer   and   later  is 


•U\ 


Fig.  4.  The  beak,  or  mouth-parts,  of 
the  grape  leaf-hopper.  Much  en- 
larged. 


Mayet's  Insectes  do  la  Vigne,   168. 


Bulletin  198.  the  GRAPE  LEAF-HOPPER.  181 

distributed  over  other  food  plants.  During  1907  the  grape  leaf-hopper 
was  particularly  abundant  in  many  of  the  vineyards  about  Fresno, 
and  also  in  the  lower  part  of  the  San  Joaquin  Valley  around  Lodi. 


LIFE  HISTORY  AND  HABITS. 

OVERWINTERING    ADULTS. 

During  the  colder  weather  of  winter  the  hoppers  may  be  found  in 
large  numbers  in  the  leaves  or  rubbish  in  the  vineyard,  or  along  the 
bordering  roadsides  and  fences.  Where  leaves  have  been  blown  together 
in  bunches  or  lodged  in  weeds  or  grass  over  the  vineyard  or  its  borders, 
hoppers  will  be  especially  likely  to  be  present  during  the  colder  or 
wet  rainy  days  of  the  winter  season.  They  will  also  be  found  harbor- 
ing low  down  along  the  fences  or  in  the  weeds  or  other  growth  among 
the  vines.  Alfilaria,  one  of  the  commonest  plants  in  many  California 
vineyards  in  winter,  forms  a  close  rosette  on  the  ground,  and  hoppers 
will  be  found  abundantly  under  the  low  spreading  foliage  of  this 
plant. 

Food  Habits. — The  grape  leaf -hopper  feeds  on  a  large  variety  of 
plants  during  the  winter  season.  It  will  be  found  feeding  chiefly 
during  the  warmer  days  of  winter,  and  resting  more  or  less  dormant 
during  the  colder  or  rainy  weather.  It  attacks  practically  everything 
that  may  be  growing  in  the  vineyard  or  vicinity,  although  a  preference 
is  shown  for  certain  plants.  Alfilaria  is  readily  attacked  by  these 
insects,  and  where  hoppers  are  numerous  the  foliage  of  this  plant  will 
be  seen  to  have  a  pale  yellow  color  as  a  result  of  their  work.  The  low 
spreading  foliage  seems  to  offer  suitable  conditions  for  the  hoppers 
when  they  are  not  feeding,  so  that  they  will  be  found  on  the  underside 
of  these  plants  almost  continuously,  regardless  of  the  kind  of  weather. 
Burr  clover  is  also  readily  attacked  by  the  hoppers  in  winter,  as  well 
as  rag  weed,  dock,  wild  mustard,  alfalfa,  and  several  kinds  of  grains 
and  grasses.  They  show  a  preference,  however,  for  such  plants  as  the 
alfilaria  and  the  clovers  as  against  the  grains  and  grasses. 

The  hoppers  that  were  taken  into  the  laboratory  in  the  early  spring 
invariably  died  in  the  course  of  two  or  three  days  if  deprived  of  food. 
Under  the  same  conditions  they  were  easily  maintained  upon  alfilaria 
or  other  food.  They  were  confined  in  lantern  globes  which  were  placed 
in  the  open  window  of  the  laboratory,  so  that  the  conditions  as  regards 
temperature  and  moisture  were  not  very  different  from  that  of  the 
vineyard.  Hoppers  were  also  confined  in  lantern  globes  in  the  vineyard, 
but  in  all  cases  they  died  very  soon  without  food,  though  the  more 
dormant  they  were  the  longer  they  were  able  to  survive. 


182  UNIVERSITY   OF    CALIFORNIA EXPERIMENT   STATION. 

Many  of  the  hoppers  succumbed  to  long  continued  wet  weather  or 
other  unusual  conditions  in  winter.  After  about  two  weeks  of  almost 
continuous  rain  we  have  counted  as  many  as  700  dead  hoppers  under 
a  single  bunch  of  alfilaria.  This  mortality  may  be  partly  accounted  for 
because  of  unsuitable  conditions  for  obtaining  food,  though  the  direct 
effect  of  exposure  to  such  conditions  is  probably  the  more  important 
factor. 

Relation  of  Food  to  Development  and  Activity. — The  activity  of  the 
insects  is  dependent  primarily  upon  food  and  temperature,  and  the 
latter  largely  influences  the  former.  No  matter  how  much  nutritious 
food  may  be  available,  if  the  temperature  is  sufficiently  low  they  become 
dormant  and  are  revived  only  upon  the  rise  of  temperature ;  but  once 
they  become  active  through  the  influence  of  a  higher  temperature,  they 
require  food  to  maintain  their  activity. 

Influence  of  Temperature  upon  Activity. — On  the  warm  days  of 
winter  the  hoppers  are  very  active  and  fly  up  in  large  numbers  before 
a  person  as  he  walks  through  the  vineyard.  On  the  contrary,  on  a 
cold  or  wet  day  they  may  only  be  disturbed  by  actually  moving  the 
object  upon  which  they  are  resting,  and  then  they  will  fly  but  a  very 
short  distance, — not  more  than  a  foot  or  two  generally.  It  is  possible 
during  such  days  to  pick  up  the  leaves,  with  a  dozen  or  more  hoppers 
resting  on  the  under  surface,  and  place  them  in  a  cyanide  bottle  without 
disturbing  them.  They  are  most  active  during  the  warmer  portions  of 
the  day, — from  nine  or  ten  o'clock  in  the  morning,  when  the  dew  is 
dried  from  the  leaves,  until  three  or  four  in  the  afternoon. 

Experiments  carried  on  in  the  laboratory  to  determine  the  effect  of 
temperature  on  overwintering  adults  indicated  that  a  temperature  of 
110°  F.  was  nearly  always  fatal.  These  experiments  consisted  in  con- 
fining the  hoppers  in  a  double  glass  vial  and  heating  gradually  with 
artificial  heat.  A  small  homo  vial  was  contained  within  a  larger  one, 
and  a  thermometer  extended  through  the  corks  of  both  vials  so  that  the 
bulb  was  contained  in  the  center  of  the  inner  vial  with  the  hoppers. 
Cotton  was  placed  in  the  bottom  of  this  vial  to  prevent  them  from 
coming  in  contact  with  the  glass  when  they  would  fall  down.  The 
whole  apparatus  prevented  so  far  as  possible  the  unequal  heating  of 
the  sides  of  the  vial  as  compared  with  the  air  in  the  interior. 

In  some  of  the  experiments,  as  given  in  the  table  below,  the  tem- 
perature was  first  reduced  by  ice  and  salt  to  30° F.  or  lower,  and 
suddenly  raised  again  to  a  point  at  which  all  the  insects  were  killed. 
By  consulting  the  table  it  will  be  seen  that  they  became  dormant  at 
60    to  65°P.  and  revived  again  at  about  70°F.    At  80°  to  90°F.  the  first 


Bulletin  198. 


THE  GRAPE  LEAF-HOPPER. 


183 


of  them  would  be  killed  by  the  heat.  The  optimum  temperature  under 
these  conditions  was  between  70°  and  85°F.  The  temperature  of  the 
room  during  the  experiments  was  between  65°  and  75 °F.  In  most  of 
the  experiments  it  was  the  ordinary  air  of  the  room,  as  regards 
humidity,  but  in  some  a  moist  plug  of  cotton  was  contained  in  the  vial 
with  the  insects,  and  thus  the  humidity  was  considerably  increased. 
The  experiments  in  detail  are  tabulated  below: 


Temperature  Experiments. 


Date. 

__ 

X 
CD 

B 

CD 

<rt- 
CO 

T>  05 

-»  a 
E- 

B 

►d  o 

CD  o 
P 

?s 

•  B 

a 

P 

a 

< 
CB 

P 

*_ 

O  __ 

B^ 

<° 

CD  P 

C_t3 

O  CD 

< 

CO 

P 

CO 

CD 
Pi 

F 

SB 
CO 

o 

CD 

p 
pi 

p 

CD  P 
<-i  CD 

i° 

CD    >-h 

13 
rt__ 

:  x 

1907— March  20    

1 

2 
3 
4 

5 

6 

7 

8 

9 

10 

11 

12 

13 

14 

15 

16 

17 

18 

7 
8 
8 
8 
8 
8 
8 
8 
8 
7 
6 
6 
6 
6 
10 
6 
7 
8 

0 

66 
66 

70 
72 
72 
72 
72 
72 
70 
68 
70 
70 
70 
70 
70 
72 
72 
72 

O 

0 

o 

o 

o 

85 

90 

95 

95 

100 

110* 

105* 

100* 

100 

105 

87 

86 

84 

80 

84 

105 

100 

105 

lfo 

110 
110 
110 
110 
120 
115 
110 
110 
110 
102 
94 
110 
114 
102 
120 
110 
110 

3m 

March  20        ________ 

4 

March  20 

10 

March  20    _     _ 

6 

March  20 

5 

March  20 

5 

March  20 

6 

March  20 

8 

March  23      -  _ 

50 
60 
65 
65-60 
66 
60 
62 

50-40 
50-45 
60-50 
62-55 
64-56 
60-54 

30 
45 
35 
25 
30 
40 
28t 

70 

70 

76 
74-8 
64-72 
57-66 
65-72 

15 

March  23      _  _ 

12 

March  23 

10 

March  23 

13 

March  23 

11 

March  23 

15 

March  23    .. 

20 

March  23 

March  23 

March  23  _ 

Vial  kept  moist  by  wet  plug  cotton. 


tHeld  for  10  m. 


In  the  column  ' '  Inactive  at "  is  indicated  when  the  hoppers  ceased 
moving  about,  and  in  the  column  ' '  Active  at ' '  when  they  first  regained 
their  locomotive  powers.  The  general  conclusions  suggested  by  these 
experiments  are  as  follows: 

A  rise  in  temperature  to  110°F.,  and  in  one  or  two  cases  to  120°F., 
invariably  killed  the  hoppers.  "With  moisture  in  the  tube  they  appeared 
to  withstand  a  slightly  higher  temperature.  Cold  to  as  low  as  25 °F. 
had  no  effect  upon  them  except  to  make  them  temporarily  dormant. 
When  they  were  subjected  again  to  the  higher  temperature  they  were 
killed  the  same  as  if  started  from  the  room  temperature,  except, 
apparently,  to  make  the  first  succumb  at  a  lower  temperature.  The 
practical  bearing  of  these  experiments  can  hardly  be  interpreted  beyond 
the  fact  that  a  sudden  rise  in  temperature  may  be  fatal  to  some  of  the 
insects.  In  this  the  rather  unnatural  condition  of  dry,  artificial  heat 
must  also  be  taken  into  consideration. 


184 


UNIVERSITY  OF   CALIFORNIA EXPERIMENT   STATION. 


Proportion 

of  the  Sexes  of  Overwintering  Hoppers. 

Collected. 

Number  of 
Specimens 
Examined. 

Females. 

Males. ' 

Percentage 
Females. 

Percentage 
Males. 

March    6th  _ 

1,500 
130 
272 
127 
134 

675 

65 

175 

72. 
100 

825 
65 
97 
55 
34 

45 

50 

64.4 

57 

74.6 

55 

March  28th  _. 

50 

April    12th 

April    19th 

April    29th  . 

35.6 

43 

25.4 

Totals  and  av.  percentage- 

2,163 

1,087 

1,076 

50.26 

49.74 

Fig.  5.  Tip  of  abdomen  of  female  grape  leaf-hopper, 
showing  ovipositor.  The  black  tipped  appendages, 
the  cerci,  obscure  the  other  parts  of  the  ovipositor 
shown  in  Fig.  6  below.     Greatly  enlarged. 


It  will  be  seen  from  the  average  percentage  in  the  above  table  that 
there  is  practically  no  difference  between  the  numbers  of  the  sexes, 

so  that  we  may  con- 
clude that  both  sexes 
are  able  to  withstand 
the  winter  conditions 
equally  well. 


Migrations. — When 
plowing  is  begun  in 
the  vineyard  in  the 
spring,  before  the 
foliage  appears  on  the 
vine,  the  food  supply 
— consisting  of  what- 
ever vegetation  may 
be  growing  —  is 
turned  under  and 
most  of  the  hoppers  are  obliged  to  look  elsewhere  for  food.  Some  of  the 
insects  remain  in  the  vineyard  and  subsist  upon  what  little  growth  may 
be  left  by  the  plow.  The  larger  number,  however,  must  look  elsewhere 
for  food,  and  this  is  generally  found  in  the  immediate  vicinity,  usually 
around  the  borders  of  the  vineyard.  We  have  seen  all  the  vegetation 
growing  along  the  roadsides  of  badly  infested  vineyards  completely 
deprived  of  the  green  coloring  matter.  After  the  vineyard  was  plowed 
the  hoppers  continued  to  feed  here,  largely,  until  the  vines  came  into 
leaf,  when  they  migrated  back  into  the  vineyards.  These  are  the  only 
distinct  movements  we  have  observed  with  the  overwintering  hoppers 
in  the  spring. 

Time  they  Attack  the  Vine. — The  first  observed  feeding  on  the  grape 
foliage  at  Lodi  during  1907  was  March  28th,  on  an'  old  Mission  vine- 
yard that  was  considerably  in  advance  of  the  other  surrounding  vine- 
yards. A  week  or  two  later,  however,  the  foliage  in  many  vineyards 
was  far  enough  along  to  attract  a  good  many  of  the  hoppers  from  their 


Bulletin  198. 


THE  GRAPE  LEAF-HOPPER. 


185 


varied  winter  food  plants.     In  1908  an  occasional  hopper  was  found 
on  vines  in  the  Sonoma  Valley  as  early  as  March  18th. 


Do  they  Feed  Exclusively  on  the  Vinef — Once  they  begin  to  feed 
upon  the  vine  they  do  not  leave  it  for  other  food  unless,  of  course,  they 
incidentally  happen  to  find  themselves  in  other  situations.  During 
two  or  three  weeks  while  the  vine  is 
coming  into  foliage,  some  hoppers  may 
be  found  on  the  vine  and  others  on 
the  winter  food  plants,  but  those  that 
are  still  feeding  on  the  other  vegeta- 
tion have  not  yet  found  their  way  to 
the  vines.  It  may  be  a  couple  of 
weeks  after  the  first  foliage  appears, 
therefore,  before  all  the  hoppers  will 
be  found  on  the  vine;  but,  once  they 
begin  to  feed  on  the  grape,  they  remain  until  the  vine  becomes  dormant 
at  the  end  of  the  season. 


Fig.  6.  The  two  pairs  of  valves  of  the 
ovipositor  with  which  the  insect 
inserts  its  egg  into  the  leaf  tissues. 
Greatly  enlarged. 


Habits  on  the  Vine. — While  the  leaves  are  still  expanding  and  not 
yet  affording  much  protection  the  hoppers  will  be  found  most  commonly 
„  on  the  concave  side  of  the  leaves  that 

are  not  yet  fully  expanded,  or  on  the 
leaves  near  the  base  of  the  vine,  where 
they  are  not  so  completely  exposed. 
At  this  period  they  were  not  observed 
to  move  about  to  any  extent,  and 
seemed  to  be  pretty  well  occupied 
with  feeding". 


Copulation  and  Oviposition.  —  On 
April  30,  1907,  they  were  observed 
pairing  for  the  first  time.  This  was 
approximately  three  weeks  after  they 
had  begun  to  feed  upon  the  vines. 

The  first  eggs  were  seen  in  the 
leaves  on  May  4th,  and  from  this  date 
on  the  hoppers  were  laying  eggs 
almost  continuously.  Egg  laying 
occurs  then  just  about  one  month  after  feeding  begins  on  the  vine. 
The  eggs  are  remarkably  well  tucked  away  in  the  leaf  tissues  by  means 
of  a  sharp  lance-like  ovipositor,  as  shown  in  figures  5  and  6. 


Fig.     7. 

grape 


Tip     of     abdomen 
leaf-hopper.      Much 


186 


UNIVERSITY   OF    CALIFORNIA EXPERIMENT   STATION. 


THE    EGG. 

Description  and  Appearance. — The  eggs  of  the  grape  leaf -hopper  are 
very  minute  objects  about  three  hundredths  of  an  inch  long  and  about 
one  third  as  wide.  They  are  slightly  bean-shaped,  as  shown  in  figures 
8  and  9.  As  they  are  situated  naturally  in  the  leaf,  within  the  tissues, 
they  are  difficult  to  detect  unless  one  is  familiar  with  their  appearance. 
If  the  light  is  at  the  right  angle  the  epidermis  will  be  seen  to  be  raised 
and  slightly  more  transparent  than  the  surrounding  tissue,  and  the 
form  of  the  egg  distinguished  beneath.    "We  occasionally  met  growers  who 

claimed  to  have  observed 
the  eggs  on  the  underside 
of  the  leaf;  but  they  were 
mistaken  in  thinking  that 
little  transparent  droplets 
of  sap  were  the  eggs  of  the 
hopper.  These  are  exuda- 
tions of  sap  which  usually 
occur  along  the  larger 
veins,  and  do  resemble 
somewhat  an  insect  egg. 
The  outer  surface  of  these 
droplets  of  sap  soon  hard- 
ens or  becomes  viscid  on 
exposure  to  the  air,  thus 
resembling  the  shell  of  an 
egg  and  making  the  simi- 
larity more  complete. 

Where  Laid.  —  Harris,1 
in  1841,  stated  that  the 
eggs  of  the  hopper  were 
laid  on  the  leaves,  but  this 
statement  appears  not  to  have  been  substantiated  by  actual  observation. 
Townsend2  in  1891  supposed  that  the  drops  of  sap,  mentioned  above, 
represented  the  egg  punctures  of  these  insects,  but  this  is  now  known 
to  be  erroneous.  Marlatt3  in  1895  stated  that  "the  eggs  are  thrust  by 
the  female  singly  into  the  substance  of  the  leaf  on  the  lower  side,  either 
into  the  midribs  and  large  veins  or  in  the  intervening  spaces."  Photo- 
graphs were  taken  of  the  eggs  in  the  leaf  in  1898  by  Professor  Wood- 
worth  of  this  station,  and  these  are  still  on  file  here.    The  first  complete 


1                 *-•--, 

Iff  $*&& 

■\~f    / 

i  "S  '  '  ■ .  '*<     7 

!       -    .    .      4 

L 

Fig.  8.  The  egg  of  the  grape  leaf-hopper  photo- 
graphed in  its  natural  position  within  the  tissues 
of  the  leaf.  The  circular  spot  at  the  top  repre- 
sents the  eye  of  the  developing  nymph  within. 
Greatly  enlarged. 


1  Insects  Injurious  to  Vegetation,  Flint  Ed. 

2  Bulletin  No.  3,  N.  M.  Aj?r.  Exp.  Sta. 

3  U.  S.  D.  A.  Yearbook,  1895,  p.  402. 


p.  228. 


Bulletin  198. 


THE   GRAPE   LEAF-HOPPER. 


187 


account  of  the  egg  and  the  first  published  pictures   were  given   by 
Slingerland1  in  1901. 

It  is  now  very  well  known  that  the  eggs  of  this  insect  are  laid  just 
beneath  the  epidermis  on  the  underside  of  the  grape  leaf.  This  is  by 
far  the  most  usual  position,  though  they  were  occasionally  found  on 
the  upper  surface.  They  are  generally  distributed  over  the  leaf  surface, 
and  occupy  no  special  position  in  relation  to  the  veins  or  ribs  of  the 
leaf.  Some  will  be  found  in  the  tissue  of  the  rib  itself,  a  good  many 
along  the  side  of  the  ribs,  and  others  scattered  about  over  the  general 
surface.  They  will  be  found  also  around  the  very  edge  of  the  leaf. 
In  thousands  of  eggs  seen  during  the  summer 
we  failed  to  find  any  arranged  in  rows  as  was 
found  by  Slingerland  in  New  York.2  '  The  six 
or  seven  eggs  laid  in  a  row  parallel  with  one 
another  would  represent  a  single  laying  of  a 
hopper,  and  there  is  no  reason  why  this  should 
not  be  done  occasionally,  but  it  is  not  the 
usual  occurrence  here.  We  have  found  them 
with  two  or  sometimes  three  arranged  more 
or  less  parallel,  but  never  more  than  this  num- 
ber. In  our  individual  breeding  cages,  where 
we  obtained  several  hundred  eggs,  and  where 
the  space  was  limited,  they  were  promis- 
cuously scattered  about,  one  in  a  place. 

We  confined  several  hoppers,  taken  in  pairs, 
and  liberated  these  in  cages  on  currant,  black- 
berry, loganberry  and  almond,  peach,  cherry, 
and  a  few  other  plants,  but  did  not  succeed 
in  obtaining  eggs  from  these  food  plants.  In 
most  cases  the  insects  were  found  dead  when  the  cages  were  examined 
three  or  four  weeks  later.  We  selected  the  particular  plants  named 
because  they  were  convenient,  and  not  because  the  eggs  would  be  more 
likely  to  be  laid  on  these  than  on  other  plants.  Possibly  more  nearly 
related  plants,  botanically,  would  be  found  suitable  for  oviposition. 
The  Virginia  creeper  is  said  to  be  readily  attacked  by  this  insect,3  and 
we  presume  eggs  are  laid  on  this  plant.  Since,  however,  this  species  is 
a  grape  pest  exclusively,  that  is,  during  the  growing  season,  and  all  the 
experience  indicates  that  it  feeds  only  upon  the  grapevine,  it  may  be 
stated,  so  far  as  the  economics  of  the  insect  is  concerned,  that  the  eggs 
are  laid  only  in  the  leaves  of  the  grape. 


Fig.  9.  The  egg  dis- 
sected from  the  leaf 
and  photographed  on 
a  microscope  slide. 
Particles  of  leaf  tissue 
are  shown  still  ad- 
hering to  the  egg. 
Greatly    enlarged. 


1  Cornell  Agr.  Exp.  Sta.  Bull.  215. 

2  Slingerland,  Bull.  215,  Cornell  Exp.  Sta. 

3  Gillette,  Colo.  Sta.  Rept.  1900. 


188 


UNIVERSITY   OF   CALIFORNIA EXPERIMENT   STATION. 


Number. — The  number  of  eggs  which  are  laid  by  this  insect,  so  far 
as  we  have  been  able  to  find,  has  not  been  previously  recorded.  It 
has  been  stated  approximately  as  one  hundred,  and  this,  so  far  as  our 
experiments  went  this  year,  is  not  very  far  from  correct.  We  were  able 
to  make  individual  records  of  a  number  of  hoppers,  and  found  that  the 


Fig.  10.  Experimental  vine  used  in  the  laboratory  for  obtaining  data  on  the 
life-history  of  the  hopper.  Cages  used  for  confining  the  insects  are 
shown  on  the  leaves. 

number  laid  varied  from  forty  to  one  hundred  and  twenty-one.  These 
were  under  laboratory  conditions,  but  not  very  different  from  that  of 
the  vineyard.  The  hoppers  were  confined  in  cages  attached  to  the  grow- 
ing leaves,  as  indicated  in  figure  10. 

These  cages  were  made  by  cutting  a  square  or  rectangular  opening 
in  a  piece  of  cardboard,  on  the  underside  of  which  velvet  was  glued 
with  pile  side  outward.     This  rested  on  the  surface  of  the  leaf  and  on 


Bulletin  198. 


THE  GRAPE  LEAF- HOPPER. 


189 


the  opposite  side;  for  the  purpose  of  holding  the  leaf  firmly  against 
the  cage,  a  piece  of  transparent  gelatine  was  used,  it  being  cut  to  cor- 
respond with  the  pasteboard  on  the  opposite  surface.  These  were 
held  together  on  the  leaf  by  means  of  ordinary  paper  clips.  Strips 
of  fairly  thick  paper  were  glued  on  the  upper  side  of  the  pasteboard, 
leaving  one  edge  free,  under  which  an  ordinary  cover  glass  could 
be  pushed.  These  cover  glasses  could  be  readily  changed  and  kept  clean, 
and  the  specimens  could  be  easily  examined,  if  necessary,  with  a  com- 
pound miscroscope.  Only  forty  eggs  were  laid  by  two  or  three  hoppers, 
but  these  probably  died  prematurely.  This  number  was  laid  in  about 
two  weeks,  which  is  a  shorter  period  than  most  hoppers  evidently  live. 
One  laid  ninety-six,  two  one  hundred  and  ten,  and  one  one  hundred 
and  twenty-one.  Since  our  observations  in  the  field  indicate  that  most 
of  the  hoppers  continue  to  lay  eggs  for  one  to  two  months,  the  number 
of  eggs  laid  will  probably  average  from  seventy-five  to  one  hundred 
and  twenty-five. 

Rate  of  Egg  Laying. — In  the  case  of  three  or  four  hoppers  we  were 
able  to  follow  pretty  closely  the  rate  at  which  the  eggs  were  deposited, 
and  the  total  length  of  the  oviposition  period.  The  following  tabulation 
for  one  of  these  is  given  below.    The  totals  are  carried  out  for  each  date  : 


Copulated  June  23d.    Cage  51. 


Rate  of  Oviposition. 


Date. 


Number 

of  Eggs 

Laid. 


Date  of  Appearance  of  Nymphs. 


Hatched 
Number. 


June  30 

July    2 

July    3 

July    6 

July    7 

July    9 

July  16 

July  17 

July  19 

July  22 

July  23 

July  24 

July  25 

July  26 

July  27 

July  31 

August   1 

August  2 

August  4 

August  7 

August   9 

August  12 

August  16 

August  17,  hopper  dead. 


13 
14 
19 
35 
35 
45 
57 
63 
68 
75 
75 
79 
79 
79 
79 
85 
85 
85 
91 
105 
107 
111 
121 


July  10. 
July  17. 
July  18. 
July  19. 
July  20. 
July  22. 
July  23. 
July  24. 
July  26_ 
July  27- 


13 
40 
43 
49 
52 
53 
58 
60 
62 
63* 


♦Total  laid  to  July  17th.    No  further  hatching  record  was  kept  for  short  intervals. 


Incubation  Period. — A  large  number  of  hoppers  were  liberated  on 
our  experimental  vines  at  9  a.   m.   May  29th,   and  removed  at  noon 

2— Bul.    198 


190  UNIVERSITY   OF   CALIFORNIA EXPERIMENT   STATION. 

on  May  30th.  About  twenty  eggs  were  laid  on  the  vines  within  this 
period  and  the  time  for  hatching  noted.  About  half  of  these  eggs 
were  enclosed  in  individual  cages  and  an  accurate  record  kept  on  the 
whole  number.  The  first  nymph  hatched  on  June  17th  and  the  last 
June  20th,  thus  requiring  a  period  of  from  seventeen  to  twenty  days 
for  the  hatching  period. 

The  above  records  were  made  on  eggs  laid  by  the  hoppers  which  had 
remained  over  winter  and  on  the  dates  given.  There  was  a  great 
difference  however  in  the  time  required  for  hatching  of  the  eggs  from 
the  spring  brood.  The  observations  were  made  during  July  and  August 
and  included  records  on  two  or  three  hundred  eggs.  The  period 
required  for  hatching  here  was  from  eight  to  twelve  days,  all  of  the 
two  or  three  hundred  eggs  coming  within  this  limit.  We  can  account 
for  the  difference  only  in  the  higher  temperature  of  the  later  months 
or  in  the  character  of  the  eggs  from  the  two  broods.  There  was  not 
much  difference  between  the  temperature  in  June  and  July  in  the 
Lodi  section,  hardly  enough  to  account  for  all  the  difference  in  embry- 
onic development.  It  may  be  possible  that  the  vigor  of  the  adults  and 
the  increased  development  of  the  egg  when  laid  will  account  for  this 
difference  over  the  spring  brood. 

The  time  required  for  the  eggs  to  mature  in  the  ovaries  was  de- 
termined as  from  five  to  seven  days.  A  number  of  pairs  in  coitu  were 
liberated  in  the  cages  and  the  first  eggs  laid  in  five  to  seven  days  later. 

Percentage  of  Eggs  that  Hatch. — The  table  indicating  rate  of  ovipo- 
sition  on  page  above  shows  that  of  the  first  sixty-three  eggs  laid  every 
one  hatched.  The  hatching  was  less  accurately  kept  for  the  remainder, 
but  we  are  quite  sure  that  every  egg  laid  by  this  particular  hopper 
brought  forth  a  nymph.  In  the  case  of  forty  eggs  laid  by  another 
hopper,  all  hatched.  With  the  layings  from  most  of  the  hoppers  in  our 
breeding  cages  a  very  high  percentage  of  the  eggs  matured.  This  was 
not  true  of  all,  however.  In  one  case  a  hopper  laid  a  total  of  thirty-five 
eggs,  scattered  along  over  a  period  of  three  weeks,  and  only  five  out 
of  the  thirty-five  hatched.  In  another  case  fourteen  eggs  were  laid  by 
an  individual  and  none  hatched.  This  experience  in  the  laboratory 
of  a  very  large  percentage  of  mortality  in  some  layings  was  also 
observed  in  the  field.  On  one  side  of  a  particular  vineyard  where 
hoppers  were  exceedingly  abundant  in  1907,  the  worst  infested  field 
seen  during  the  season,  there  was  a  very  great  mortality  in  the  egg 
stage.  On  a  single  leaf  taken  from  this  particular  area  we  have 
counted  a  total  of  seven  hundred  and  forty-seven  eggs  that  failed  to 
mature.  These  could  be  very  readily  detected  on  the  leaf  by  the  dead 
epidermis  covering  them,  which  was  dark  brown  to  black  in  color. 
The  leaf  was  thoroughly  sprinkled  with  these  black  areas,  and  showed 


Bulletin  198.  THE  GRAPE  LEAF-HOPPER.  191 

fairly  well  in  a  photograph,  but  not  distinct  enough  to  reproduce  here. 
Upon  examining  these  eggs  that  failed  to  hatch  they  appeared  not  to 
have  started  their  course  of  development,  or  in  other  words,  were 
infertile.  The  egg  itself  was  generally  found  to  be  fresh  and  intact, 
the  black  color  on  the  leaf  being  due  in  most  cases  entirely  to  the 
epidermis  over  the  egg.  This  was  in  a  vineyard  where  the  hoppers 
appeared  in  innumerable  numbers  in  the  early  spring,  and  the  eggs  laid 
were  from  hoppers  that  had  remained  over  winter.  The  mortality  in 
the  egg  stage  reduced  their  numbers  to  a  very  appreciable  extent. 
What  was  true  of  this  one  vineyard  in  1907  was  observed  very  generally 
in  the  vineyards  around  Lodi  in  1908. 

We  tried  to  account  for  this  failure  of  the  eggs  to  mature  from  a 
number  of  causes,  but  the  matter  is  still  unsatisfactorily  settled.  We 
first  started  on  the  supposition  that  something  in  the  nature  or  make-up 
of  the  leaf,  or  a  bacterial  or  fungous  disease  of  the  egg,  might  be 
responsible.  The  underside  of  the  leaves  of  these  vines  were  covered 
over  more  or  less  with  pubescence  or  hairs.  That  this  might  have 
some  effect  in  a  mechanical  way  by  holding  moisture  and  thus  fur- 
nishing the  best  conditions  for  producing  disease  was  not  borne  out, 
since  the  same  conditions  were  noted  elsewhere  with  practically  no 
mortality.  The  hoppers  themselves  seemed  to  be  as  healthy  as  those 
elsewhere,  and  a  miscroscopical  examination  showed  nothing  unusual. 
That  the  eggs  were  infertile  seems  evident,  but  the  exact  cause  in  this 
particular  area  is  not  yet  accounted  for.  Males  were  present  in  their 
normal  numbers,  and  our  experiments  thus  far  indicate  that  they  do 
not  reproduce  parthenogetically. 

The  exact  causes  of  such  conditions  as  these  will  largely  account  for 
the  sudden  disappearance  of  the  hoppers  after  having  become  very 
abundant.  It  is  well  known  that  hoppers,  like  many  other  insects, 
have  their  ups  and  downs  as  regards  numbers.  In  1897  the  hoppers 
were  so  abundant  about  Fresno  during  the  winter  that  the  people 
appealed  to  the  University  for  aid  in  combating  them  for  the  approach- 
ing season.  An  investigation  was  undertaken  by  Professor  Woodworth 
and  headquarters  opened  for  a  season 's  campaign ;  the  hoppers  appeared 
in  great  numbers  in  the  spring,  as  was  to  be  expected  from  their 
abundance  in  winter,  but  the  majority  failed  to  lay  eggs  and  none 
appeared  to  be  normally  productive,  and  as  a  result  there  were  scarcely 
enough  of  the  new  generation  produced  to  furnish  good  material  for  the 
investigation.  From  what  is  known  of  the  history  of  the  pest  in  the 
State,  this  is  an  example  of  what  occurs  more  or  less  periodically. 

Effect  of  Oviposition  on  the  Leaf. — So  far  as  we  could  see  the 
puncturing  of  the  leaf  tissues  for  egg  laying  had  no  appreciable  effect 
on  the  functions  of  the  leaf.    In  many  cases  it  was  hard  to  tell  where 


192 


UNIVERSITY   OF   CALIFORNIA EXPERIMENT   STATION. 


an  egg  had  been  after  hatching.  In  others  the  epidermis  was  blackened. 
In  the  case  of  the  mortality  in  the  eggs,  already  referred  to,  these 
spots    were    very    numerous  ^ 

and  probably  interfered 
somewhat  with  the  normal 
functions  of  the  leaf,  but 
ordinarily  these  small  punc- 
tures have  no  noticeable 
effect  on  the  leaf. 

THE    NYMPH. 

The  young,  immature 
hopper  is  called  a  nymph. 
It  differs  from  the  adult 
chiefly  in  the  fact  that  the 
wings  are  not  fully  de- 
veloped. These  are  grad- 
ually acquired  with  each  of 
the  five  successive  molts 
until  after  the  last  stage, 
when  the  adult  with  fully 
formed  wings  appears.  The 
stages  may  be  easily  recog- 
nized by  the  development  of 
the  wing  pads.  The  relative 
size  is  indicated  in  the  pho- 
tographs (Fig.  11),  which 
were  all  taken  under  the 
same  magnification. 

The  Hatching  Process. — 
Several  young  nymphs  were 
observed  in  the  process  of 
emerging  from  the  egg  cov- 
ering, and  it  generally  re- 
quired from  ten  to  fifteen 
minutes  for  this  process. 
After  remaining  quiet  for 
a  few  minutes  just  outside 
the  eggshell  they  would 
move  about  until  they  found 
a  suitable  place  for  insert- 
ing their  beaks  for  food, 
where    they    would    remain 


Bulletin  198. 


THE  GRAPE  LEAF-HOPPEK. 


193 


quiet  for  some  time.  For  a  few  days  before  the  eggs  hatch  there  is  a 
conspicuous  dark  spot  at  one  end  of  the  egg,  which  represents  the 
eye  of  the  developing  nymph  within.  It  is  at  this  end  that  the  egg 
covering  is  broken  and  the  nymph  makes  its  way  out. 

First  Stage. — The  young  nymph  upon  hatching  from  the  egg  is  a 
very  small  semi-transparent  whitish  creature  with  conspicuous  red  eyes. 
The  wing  pads  are  invisible.  The  head  and  thorax  appear  large  in 
proportion  to  the  abdomen,  and  the  insect  walks  in  a  more  or  less 
wabbling  manner.  The  length  of  the  period  from  hatching  to  the 
first  molt  is  four  days. 

Second  Stage. — After  the  first  molt  the  conspicuous  red  pigment  in 
the  eyes  is  partly  lost,  and  the  form  of  the  body  becomes  more  cylin- 
drical. Indications  of  yellow  markings  appear  on  the  thorax,  and  the 
wing  pads  just  begin  to  appear  as  lateral  buds.  The  length  of  this 
stage  is  two  days. 

Third  Stage. — The  markings  of  the  thorax  become  a  little  more 
prominent,  and  the  wing  pads  appear  as  buds  extending  posteriorly  to 
the  caudal  margin  of  the  first  segment  of  the  abdomen.  The  hind 
margin  of  the  thorax  is  curved  or  arched,  as  a  result  of  the  wing  pads 
projecting  posteriorly  at  the  sides.  The  length  of  this  stage  is  three 
days. 

Fourth  Stage. — There  is  not  much  change  in  the  general  appearance, 
except  that  the  wing  pads  are  now  conspicuously  larger  and  extend 
to  the  caudal  border  of  the  second  abdominal  segment.  The  length  of 
this  stage  is  four  days. 

Fifth  and  Last  Stage. — The  wing  pads  now  extend  to  the  caudal 
border  of  the  third,  or  to  the  middle  of  the  fourth,  abdominal  segment. 
The  length  of  this  stage  is  five  days. 

After  the  fifth  molt  the  fully  formed  wings  appear,  extending  to 
beyond  the  tip  of  the  abdomen. 

Some  of  the  life-history  work  carried  on  to  determine  the  number 
and  length  of  the  nymphal  stages  is  indicated  in  the  following  table : 


Cage 
No. 


52 

53 

54 

55 

56 

57 

60a 

62 

63 


Hatched  between- 


9  p.  m.  July  17  to  9  a. 
4  p.  m.  July  17  to  9  a. 
9  p.  m.  July  17  to  8  a. 
4  p.  m.  July  17  to  9  a. 
4  p.  m.  July  17  to  9  a. 
4  p.  m.  July  17  to  9  a. 

6  a.  m.  July  22  to  8  a. 

7  p.  m.  July  18  to  8  a. 
7  p.  m.  July  18  to  8  a. 


m.  July  18 
m.  July  18 
m.  July  18 
m.  Julv  18 
m.  Julv  18 
m.  July  18 
m.  July  23 
m.  July  19 
m.  Julv  19 


First 

Second 

Third 

Fourth 

Fifth 

Molt, 

Molt. 

Molt. 

Molt. 

Molt. 

7-22 

7-24 

7-26 

7-30 

8-4 

7-22 

7-23 

7-26 

7-30 

8-4 

7-22 

7-24 

7-26 

7-30 

8-4 

7-22 

7-24 

7-26 

8-1 

8-6 

7-23 

7-25 

7-29 

8-2 

8-6 

7-23 

7-25 

7-29 

8-2 

8-6   - 

7-26 

7-31 

8-2 

8-5 

8-11 

7-23 

7  24 

7-27 

7-30 

8-4 

7-23 

7-26 

7-30 

8-1 

8-6 

Adult 
St>ige, 
Total. 


17 
17 
17 
19 
19 
If* 
19 
16 
18 


194 


UNIVERSITY  OF   CALIFORNIA EXPERIMENT   STATION. 


Cage 
No. 

Hatched  between — 

First 
Molt. 

Second 
Molt. 

Third 
Molt. 

Fourth 
Molt. 

Fifth 
Molt. 

Adult 
Stage, 
Total. 

64 

65 

66 

66a 

67 

68 

70 

71 

69 

8  p.  m.  July  19  to  8  a.  m.  July  20 

8  p.  m.  July  19  to  8  a.  m.  July  20 

6  a.  m.  July  22  to  8  a.  m.  July  23 

6  a.  m.  July  22  to  8  a.  m.  July  23 

8  p.  m.  July  19  to  8  a.  m.  July  20 

6  p.  m.  July  19  to  8  a.  m.  July  20 

6  p.  m.  July  25  to  8  a.  m.  July  26 

6  p.  m.  July  25  to  8  a.  m.  July  26 

12  m.  July  23  to  8  a.  m.  July*24 

7-23 
7-23 
7-26 

7-27 
7-23 
7-23 
7-30 
7-30 
7-28 
7-31 

7-26 

7-26 

7-28 

7-31 

7-26 

7-26 

8-1 

8-1 

7-30 

8-2 

7-30 

7-28 
7-31 

8-1 

7-28 

7-28 

8-4 

8-4 

8-2 

8-5 

8-2 
8-1 
8-4 
8-4 
8-1 
8-1 
8-7 
8-3 
8-5 
8-8 

8-7 

8-6 

8-9 

8-10 

8-6 

8-6 

8-13 

8-13 

8-11 

8-13 

18 
17 
17 
18 
17 
17 
18 
18 
18 

72 

3  p.  m.  July  26  to  8  a.  m.  July  27 

17 

From  the  above  table  it  will  be  seen  that  the  shortest  time  required  to 
go  through  the  five  nymphal  stages  is  sixteen  days,  and  the  longest 
period  nineteen  days,  the  average  being  about  eighteen  days. 

Summarizing  the  duration  of  each  of  the  stages  as  given  above, 
it  will  be,  disregarding  fractional  days,  as  follows: 


Stage. 

Wing  Pads. 

Duration  of 
Stage. 

First    . 

Invisible      __        _.__               __          __ 

4  days 

2  days 

3  days 

4  days 

5  days 

Second      _     

As  lateral  buds_-            _      _        __          _  __ 

Third 

Extending  to  caudal  border  first  abdominal  segment  __ 
Extending  to  caudal  border  second  abdominal  segment- 
Extending  to  caudal  border  third  abdominal  segment-- 

Total -     -_        

Fourth 

Fifth 

18  days 

The  total  length  of  the  nymphal  life  of  the  grape  leaf-hopper  in 
New  York,  as  worked  out  by  Slingerland,1  is  from  thirty  to  thirty-three 
days.  This  is  a  difference  of  about  two  weeks  from  that  of  the  same 
species  in  California.  Climatic  conditions  probably  account  for  this 
difference,  although  so  far  as  temperature  is  concerned,  there  is  not 
much  difference  between  the  section  about  Lodi  in  June  and  July  and 
that  of  New  York  in  the  same  months. 

Molting. — As  a  preliminary  step  to  the  actual  shedding  of  the  skin, 
the  nymph  becomes  quiet  for  a  short  period,  then  the  old  skin  splits 
on  the  thorax  and  the  nymph  with  its  new  covering  makes  its  way 
out.  The  actual  working  out  from  the  old  skin  required  about  ten 
minutes,  and  in  a  very  short  time  thereafter  it  is  able  to  move  about 
as  usual.  Immediately  after  emerging  from  the  old  skin  the  insect  is 
white  in  color  and  fairly  transparent.  The  tracheal  system  can  be 
followed  very  readily,  especially  in  the  younger  nymphal  stages,  after 
emerging  from  its  old  integument.  During  the  process  of  emerging 
the  old  skin  seems  to  be  held  on  to  the  leaf  by  the  claws  of  the  feet, 
and  these  often  remain  for  some  time  attached  to  the  leaf.  The  last 
nymphal  skin,  however,  is  much  more  firmly  attached  than  the  earlier 

'Cornell  Exp.  Sta.  Bull.  No.  215,  p.  92. 


Bulletin  198. 


THE  GRAPE  LEAF-HOPPER. 


195 


east  skins,  and  later  in  the  season  these  last  skins  will  be  about  all  that 
will  be  seen  adhering  to  the  leaf.     The  accompanying  picture,  Fig.  12 

(and  on  the  cover  of  this  bulletin),  photographed  by  Mr.  W.  B.  Parker, 
shows  one  of  these  cast  skins  and  the  adult  which  emerged  from  it. 

Habits  of  Feeding. — The  young  nymph  upon  hatching  from  the  egg 
soon  finds  a  suitable  place  on  the  leaf  for  inserting  its  beak,  and  begins 
to  feed  on  the  plant  juices.  The  majority  of  them  remain  during  the 
earlier  nymphal  stages  on  the  same  leaf  from  which  they  originally 
emerged,  but  later  there  is  more  or  less  migration  to  other  leaves  on  the 
vine;  but  probably 
a  large  number  re- 
main throughout 
their  nymphal  life 
on  the  same  leaf. 

Leaves  which  had 
contained  large 
numbers  of  eggs, 
some  of  which  were 
hatched  and  some 
not,  were  always 
seen  to  be  well 
stocked  with  nymphs, 
while  other  leaves 
immediately  adjoin- 
ing were  free  from 
both  eggs  and 
nymphs.  Leaves 
which  had  already 
lost  most  of  their 
green  coloring  mat- 
ter    were     seen     to 

have  nymphs  in  abundance,  while  fresh  green  leaves  near  by,  offering 
a  better  food  supply,  were  observed  to  be  very  free  from  hoppers.  Of 
course,  the  nymphs  can  not  leap  or  fly,  and  so  can  not  make  their 
way  from  one  leaf  to  another  on  different  shoots  unless  they  happen 
to  be  touching,  or  else  crawl  down  to  the  base  of  the  shoot  and  up  on 
the  new  one.  Leaves  on  the  same  shoot  were  observed  to  have  a  great 
difference  in  the  number  of  hoppers,  always  being  most  abundant  on 
the  older  and  paler  colored  leaves,  where  the  most  eggs  were  to  be 
found. 

Transfer  to   Other  Food  Plants. — In   order   to   determine  whether 
nymphs  would  mature  if  transferred  to  other  food  plants  than  the 


Fig.    12.     Adult  grape  leaf-hopper  just  emerged. 


196  UNIVERSITY   OF   CALIFORNIA EXPERIMENT   STATION. 

grape,  we  confined  large  numbers  of  nymphs  in  all  stages  on  apple, 
almond,  currant,  blackberry,  and  peach,  and  in  each  case  practically 
all  completed  their  development  in  due  course.  Some  of  these  were  left 
on  their  food  plants  long  enough  to  pair  and  lay  eggs,  but  we  were 
unable  to  find  any  evidence  of  eggs  having  been  deposited.  In  another 
place  it  has  been  stated  that  adult  females  which  were  known  to  be 
fertilized  failed  to  lay  eggs  on  these  same  plants.  It  may  be  inferred 
then  that  nymphs  will  mature  on  other  food  plants,  but  it  is  at  least 
unusual,  if  ever,  that  eggs  will  be  laid  elsewhere  than  on  the  grape. 

THE   ADULT. 

Time  of  Reaching  Maturity.- — The  first  adults  from  the  spring  brood 
at  Lodi  were  observed  on  June  8,  in  1907,  and  on  June  12,  1908,  this 
being  about  two  months  after  they  had  begun  to  feed  on  the  vine  in 
the  spring.  By  the  last  of  June  newly  emerged  adults  were  very 
common.  At  this  time  many  were  seen  pairing,  indicating  that  they 
were  fully  mature. 

Feeding  Habits. — The  habits  of  feeding  of  the  adults  are  not  very 
different  from  those  of  the  nymphs  except  that  they  move  about  more. 
They  will  be  found  in  greatest  numbers  on  the  leaves  around 
the  base  of  the  vine  and  feeding  with  the  nymphs.  All 
through  the  season  the  hoppers,  in  whatever  stage  they  may 
be,  will  be  most  abundant  in  the  interior  of  the  vine.  This 
is  probably  for  protection,  since  the  food  supply  is  not  as 
good  as  that  on  the  outside  of  the  vine,  for  the  older  and 
less  succulent  leaves  are  around  the  base  of  the  vine.  So 
far  as  the  food  is  concerned  it  would  appear  that  the  new 
Fig.  13.  The     leaves   near   the   tip   of  the   growing   shoot   would   better 

adult    grape  r  . 

leaf -hopper,     satisfy  them,  as  is  the  case  with  plant  lice  and  some  other 

enlarged  J  '  r 

d?ameters1Ve       °^  tne  SUC^ing  insects. 

Copulation  and  Oviposition. — Adults  of  the  spring  brood  were  seen 
pairing  during  the  last  of  June,  and  most  commonly  about  the  middle 
of  July.  An  occasional  pair  was  seen  during  the  first  week  in  August, 
but  after  this  none  were  seen  throughout  the  rest  of  the  season. 

Egg  laying  began  with  the  spring  brood  during  the  last  week  in  June 
in  1907  and  the  same  time  in  1908.  The  overwintering  hoppers  were 
also  still  depositing  eggs,  so  that  there  appeared  an  overlapping  of 
the  two  broods. 

Activity  and  Migrations. — While  there  was  more  or  less  moving 
about  among  the  hoppers  in  the  same  vineyard,  no  migrations  from  one 
vineyard  to  another  were  observed  until  about  the  middle  of  July.     At 


Bulletin  19S. 


THE  GRAPE  LEAF-HOPPER. 


197 


this  time,  and  later,  hoppers  were  seen  in  some  cases  flying  about  the 
farmhouses  some  little  distance  from  any  vines.  They  were  seen  at 
night,  and  when  the  weather  was  warm  and  calm.  They  appeared  not 
to  be  going  in  any  particular  direction.  Such  migrations  or  activity 
were  only  very  occasional,  and  so  far  as  we  could  see  the  numbers  in 
the  vineyards  were  not  changed.  In  the  cases  noted  there  was  no 
particular  reason  for  the  migration  on  account  of  food.  We  believe 
that  favorable  weather  conditions  caused  greater  activity  on  the  part 
of  the  insects,  and  that  they  are  just  as  likely  to  go  back  into  the 
same  vineyard  as  to  make  a  distinct  migration  in  a  definite  direction 
for  change  of  food  or  other  reasons. 

Activity  of  the  Sexes. — Both  males  and  females  seemed  to  be  equally 
active  as  seen  from  the  proportion  of  the  sexes  taken  in>  the  air 
with  a  net  when  disturbed,  and  the  fact  that  they  were  found  in  all 
situations  in  about  equal  numbers  would  seem  to  indicate  that  there 
is  no  difference  as  regards  the  activity  of  the  sexes. 


Proportion  of  the  Sexes. 


Date 


Number 

Ex- 
amined. 


Males. 


Females. 


Per  cent 
Males. 


Per  cent 
Females. 


May  20_ 
May  20_ 
May  22_ 
May  22_ 
May  22_ 
June  8- 
June  8_ 

Totals 


200 
200 
100 
308 
167 
140 
215 


1,330 


59 
75 
65 
150 
89 
75 
85 


598 


141 

125 

35 

158 
78 
65 

130 


732 


29.5 

37.5 

65. 

48.7 

53.2 

53.5 

39.5 


45 


70.5 
62.5 
35. 
51.3 

4H.8 
4H.5 
60.5 


55 


Differences  in  Coloring  Due  to  Age. — The  hoppers  in  winter  are 
distinctly  redder  in  color,  i.  e.,  the  markings  are  more  pronounced  than 
at  any  other  season.  The  reddish  color  becomes  more  conspicuous  as 
the  winter  season  approaches,  after  they  have  left  the  vine  and  began 
to  feed  upon  their  winter  food  plants.  In  the  spring  after  they  have 
been  feeding  for  a  few  weeks  on  the  vine  they  become  distinctly  paler 
in  color  again.  This  less  conspicuous  marking  is  then  maintained 
throughout  the  life  of  the  insect  surviving  the  winter.  While  they 
have  become  distinctly  paler  in  color  after  feeding  for  two  or  three 
weeks  on  the  vine  in  the  spring,  they  are  not  so  pale  colored  as  the 
newly  hatched  hoppers,  and  the  individuals  of  the  two  broods  may 
be  distinguished  for  a  time  after  their  emergence.  The  hoppers  of  the 
second  brood  that  are  on  the  vines  in  the  fall  take  on  the  more  con- 
spicuous coloring  with  the  approach  of  the  winter  season,  and  this 
more  pronounced  marking  remains  until  after  they  have  fed  for  a 
few  weeks  on  the  vine  in  the  following  spring. 


198 


UNIVERSITY  OF   CALIFORNIA EXPERIMENT   STATION. 


The  Varieties  of  the  Species  Comes. — Altogether  there  are  nine 
varieties  of  this  species  recognized  in  the  United  States.1  All  the 
specimens  taken  on  the  grape  this  year  abont  Lodi  and  Fresno,  Cali- 
fornia, were  the  typical  comes,  and  the  variety  color adensis.  The 
difference  between  these  two  varieties  is  that  coloradensis  has  a  black 
spot  on  either  side  of  the  scutellum  at  the  base,  while  in  comes  these 


Fig.    13.     A   vine    enclosed    by    a    cheese-cloth    cage,    open    at    the    top,    for 

studying  migrations. 

spots  are  wanting.  Comes  largely  predominates,  as  is  indicated  by 
the  following  table.  The  specimens  were  mounted  on  velvet  between 
two  miscroscope  slides,  and  collected  on  the  dates  given : 


Proportion  of  the  Varieties  of  the  Grape  Leaf-hopper. 

Date. 

Slide. 

Num- 
ber. 

Comes. 

Colora- 
densis. 

1—29 

1 
2 
3 
4 
5 
6 

150 
155 
145 
155 
136 
96 

134 
135 
129 
142 
122 
80 

16 

II— 17 

20 
16 

11—15    

13 

January — June     __          __. 

14 

V— 25                                            

16 

Total 

837 

742 
88.64 

95 

Percentage. -_ 

11.35 

i 

1  Gillette,  Proc.  U.  S.  N.  M.,  vol.  20,  1898,  p.  709. 


Bulletin  198.  THE  GRAPE  LEAF- HOPPER.   .  199 

Gillette,  in  the  publication  cited,  states  that  coloradensis  is  a  very 
distinctly  marked  variety  and  one  that  seems  to  be  confined  entirely 
to  the  West.  This  does  not  mean  that  it  is  limited  to  the  Pacific  coast 
states,  for  it  occurs  commonly  in  Colorado,  and  it  is  also  found  in 
Nebraska,  Kansas,  and  New  Mexico.  Specimens  of  the  California 
varieties  were  sent  to  Professor  Gillette  and  he  replied  that  they  were 
the  typical  comes  and  coloradensis,  the  same  as  he  would  collect  on  the 
grape  in  Colorado.  So  far  as  we  know,  none  of  the  other  eight  varieties 
of  the  species  have  been  recorded  from  this  State. 

The  Common  Name  of  the  Insect. — The  insect  treated  of  in  this 
bulletin  is  probably  best  known  by  the  vineyardists  of  the  State  as  the 
"thrips"  or  "vine  thrips."  This  name,  however,  is  improperly  applied 
to  this  insect,  since  the  term  "thrips"  rightly  belongs  to  insects  of 
a  different  group.  The  true  thrips,  if  they  have  any  wings  at  all,  have 
delicate  fringe  wings,  and  are  not  so  active  as  the  leaf-hopper.  The 
thrips  are  very  small,  slender  bodied  insects,  ranging  from  yellowish 
to  black  in  color,  and  will  be  most  easily  found  in  flower  cups,  where 
they  feed  upon  the  sap  of  the  different  parts  of  the  flower  as  well  as 
upon  the  leaves.  There  are  several  injurious  species  of  thrips,  but  none 
do  much  damage,  so  far  as  observed,  to  the  grape.  One  particular 
species  has  become  a  very  important  pest  to  fruit  trees  in  the  Santa 
Clara  Valley.  To  avoid  confusion,  therefore,  the  term  ' '  thrips ' '  should 
be  applied  to  such  an  insect  as  this  in  the  Santa  Clara  Valley  and 
elsewhere. 

The  common  name  of  the  insect  discussed  in  this  bulletin,  as 
adopted  by  the  Association  of  Economic  Entomologists  is  the  "grape 
leaf -hopper. "  This  is  generally  shortened  in  this  State  to  simply 
"hopper"  or  "vine  hopper,"  and  this  may  be  specific  enough  here,  since, 
when  we  speak  of  "vine"  alone  there  is  no  mistaking  the  kind  of  vine 
referred  to;  and  it  is  generally  understood  that  all  hoppers  feed  on  the 
leaf.  However,  the  correct  common  name  of  the  insect,  as  officially 
adopted,  is  the  Grape  leaf-hopper. 

Preference  for  Different  Varieties  of  Vines. — In  many  vineyards 
infested  with  vine  hoppers  it  will  be  noticed  that  certain  varieties  of 
vines  will  be  much  worse  attacked  than  certain  other  varieties.  It 
may  be  easy,  in  the  case  of  a  single  vineyard,  to  express  in  definite 
terms  the  preference  shown  by  the  hoppers  for  particular  varieties; 
but  in  another  vineyard  in  the  same  neighborhood  these  conditions  may 
be  almost  reversed,  so  that  one  is  hardly  warranted  in  making  a  general 
statement  that  will  apply  to  all  conditions  and  all  situations. 

However,  certain  facts  were  observed  which  may  indicate  a  choice 


200  UNIVERSITY  *OF   CALIFORNIA — EXPERIMENT   STATION. 

on  the  part  of  the  hoppers  for  particular  varieties  of  grapes.  In 
the  Lodi  section  the  two  chief  varieties  of  grapes  grown  are  the  Tokay 
and  the  Zinfandel.  Throughout  all  this  section,  so  far  as  we  observed, 
a  distinct  preference  was  shown  for  the  Tokay  over  the  Zinfandel. 
The  Mission  vines  are  also  readily  attacked  by  the  hoppers  in  this 
section.  In  a  particular  vineyard,  which  contained  these  three  varieties, 
the  Mission  and  Tokay  were  worst  infested, — the  Mission  a  little  worse 
than  the  Tokay,  while  the  Zinfandel  was  distinctly  the  least  infested. 
In  a  vineyard  at  Madera,  which  was  under  observation  for  some  time, 
the  vines  which  were  most  resistant  or  were  less  readily  attacked  by  the 
hoppers  were  the  Fehr-Yagos,  Zinfandel,  Alicante  Bouchet,  Petit 
Bouchet,  and  Mataro.  Of  these  the  Fehr-Yagos  and  Zinfandel  showed 
the  least  injury.  In  this  question  of  preference  for  varieties,  of  course 
the  difference  in  the  degree  of  susceptibility  of  the  varieties  to  an 
equal  attack  of  hoppers  must  be  taken  into  consideration ;  i.  e.,  some 
varieties  may  be  more  weakened  than  others,  although  the  hoppers  may 
be  present  in  equal  numbers.  The  actual  difference  in  the  numbers 
of  hoppers,  however,  may  be  very  readily  determined  by  jarring  the 
vines  and  observing  the  numbers  flying  about  them.  The  difference  in 
numbers  in  most  cases  is  so  great  that  there  is  little  difficulty  in  judg- 
ing this.  The  larger  numbers  of  hoppers  will  always  be  found  on 
the  vines  showing  the  most  injury  unless,  of  course,  it  is  on  those  vines 
that  are  so  badly  injured  that  most  of  the  food  supply  is  gone  and  they 
are  obliged  to  go  elsewhere  for  food. 


DEVELOPMENT. 

Length  of  Life  Cycles.— Hoppers  hatching  from  eggs  in  midsummer 
or  early  fall  remain  over  winter  and  attack  the  vine  as  soon  as  the 
foliage  appears  in  the  spring.  Here  they  feed  for  a  month,  after 
which  egg  laying  begins,  and  which  may  continue  for  two  months 
longer.  This  will  take  it  to  midsummer  again,  so  that  the  length  of 
this  life  cycle  is  approximately  one  year.  Large  numbers  of  overwinter- 
ing hoppers  were  enclosed  in  cheese-cloth  bags  in  the  vineyard,  and 
the  hoppers  were  observed  to  begin  dying  off  in  June,  and  by  the  last 
of  July  practically  all  were  dead.  Hoppers  hatching  from  eggs  laid 
in  May  and  June  begin  laying  eggs  upon  reaching  maturity  five  weeks 
later.  Egg  laying  continues  for  a  month  or  two  longer,  when  they  in 
turn  begin  to  die  off,  thus  making  the  length  of  this  life  cycle  from 
three  to  four  months. 

Number  of  Generations. — The  number  of  generations  of  the  insect 
as  indicated  above  is  two.  Although  these  broods  may  overlap  one 
another  they  are  very  distinct,  and,  at  least  in  the  Lodi  section  in  1907 


Bulletin  198.  the  grape  leap-hopper.  201 

and  1908,  there  was  no  indication  of  a  third  brood.  There  were  two 
well  marked  periods  of  breeding,  and  none  were  seen  pairing  excepting 
during  these  periods.  For  the  overwintering  hoppers  this  period  was 
during  the  last  week  in  April  and  the  first  two  weeks  in  May.  For 
the  summer  brood,  or  those  hatching  from  eggs  laid  in  May  and  follow- 
ing, the  breeding  period  extended  over  the  last  week  in  June  and  the 
greater  part  of  July,  the  maximum  pairing  occurring  about  July  10th. 
The  breeding  period  of  this  brood  is  thus  seen  to  be  greater  than  that 
of  the  winter  brood  because  of  the  prolonged  hatching  period  of  the 
preceding  generation,  while  in  the  case  of  the  overwintering  hoppers 
they  all  reach  maturity  at  about  the  same  time  and  pairing  takes  place 
within  two  or  three  weeks. 

The  best  evidence  of  the  number  of  broods  is  indicated  in  the  well 
defined  periods  of  breeding,  but  this  fact  is  further  strengthened  by 
the  appearance  of  the  nymphs.  A  couple  of  weeks  after  the  maximum 
breeding  young  nymphs  appeared  in  great  abundance,  while  the 
appearance  of  the  young  gradually  diminished  as  the  time  from  these 
dates  increased.  By  September  1st  very  few  young  nymphs  were  seen, 
and  all  stages  of  nymphs  were  gradually  disappearing  and  none  at  all 
were  seen  after  October  15th.  If  there  was  even  a  partial  third  brood 
it  would  be  expected  that  young  nymphs  would  be  found  up  to  the 
time  the  leaves  fell  from  the  vine ;  but  this  would  not  necessarily  indi- 
cate a  third  brood,  for  it  might  be  due  to  the  prolonged  development  of 
the  second  brood.  The  absence  of  any  pairing  of  individuals  of  the 
second  brood  during  the  late  summer  or  fall,  and  the  young  nymphs 
ceasing  to  appear  at  the  normal  time  after  the  breeding  period  of  the 
preceding  brood,  indicate  quite  clearly  that  there  are  two  generations 
of  the  insect  in  a  year. 

Comparison  of  Development  in  Other  Localities. — At  Fresno,  one 
hundred  and  thirty  miles  south  of  Lodi,  where  the  temperature  is  con- 
siderably higher  than  at  the  latter  place,  the  hoppers  go  through 
apparently  the  same  development,  although  the  different  stages  in 
the  life  cycles  appear  from  a  week  to  two  weeks  earlier  than  at  Lodi. 
Continuous  observation  was  not  made  on  the  hoppers  in  the  vicinity  of 
Fresno,  but  several  trips  were  made  to  this  section  during  the  season 
and  the  life  history  checked  with  that  of  Lodi,  except  that  it  was  a  week 
or  two  earlier.  In  a  visit  to  this  territory  on  October  20th  no  nymphs 
were  found  in  any  stage,  and  this  would  seem  to  indicate  that  there 
are  but  two  broods  as  at  Lodi. 


202  UNIVERSITY  OF  CALIFORNIA EXPERIMENT  STATION. 

NATURAL  CONTROL. 

Climatic. — The  sudden  decrease  in  numbers  of  insects  without  any 
known  specific  cause,  a  condition  frequently  observed,  is  often  attributed 
to  the  general  and  more  or  less  indiscriminate  term  "weather  condi- 
tions." Grape  leaf -hoppers,  are  known  to  occur  in  excessive  numbers 
more  or  less  periodically,  and,  for  lack  of  definite  information,  we 
ascribe  the  cause  to  climatic  conditions.  Whether  these  conditions 
have  a  direct  effect  in  reducing  the  numbers  through  exposure,  or 
through  sudden  increase  or  decrease  of  temperature,  or  through  humid- 
ity, or  the  indirect  effect  of  these  influences  in  inducing  disease,  in 
favoring  the  development  of  parasitic  and  predatory  enemies,  in 
reducing  fecundity,  or  in  unfavorably  affecting  the 
food  supply,  are  points  not  easily  determined. 

We  have,  however,  apparently  some  evidence  on  the 

direct  effect  of  unfavorable  weather  conditions  in 

reducing  the  number  of  grape  leaf -hoppers.    During 

March,  1907,  there  were  two  or  three  weeks  of  almost 

continuous   rain.     At   the   end   of   this   period   the 

hoppers  were  found  dead  in  large  numbers  in  all  the 

vineyards  in  the  Lodi  section.     Between  seven  and 

eight  hundred  dead  hoppers  have  been  counted  under 

a  single  bunch  of  alfilaria.    In  certain  vineyards  that 

Fig.  15.    The  larva  of  were  flooded  with  two  or  three  feet  of  water  the 

commonesf  predatory  hoppers  were  nearly  all  destroyed.     This  latter,  of 

enemy  of  the  hopper  course,   is   an   unusual    condition,    but   unfavorable 

in   California. 

weather   conditions   of   winter   or   early   spring   no 
doubt  destroy  large  numbers  of  these  insects. 

Parasitic. — The  grape  leaf-hopper  appears  to  be  particularly  free 
from  natural  enemies,  and  this  is  especially  true  of  parasitic  enemies. 
In  many  hundreds  of  eggs,  nymphs  and  adults  examined  and  kept  in 
breeding  cages  during  the  season  we  did  not  find  a  single  specimen 
parasitized. 

Predatory. — Most  of  the  natural  enemies  of  the  hopper  come  under 
this  category  of  predatory  or  predaceous  enemies,  but  even  this  list 
is  not  large.  The  most  common  of  these  observed  during  the  season 
was  one  of  the  aphis  lions  or  larvas  of  a  lace-wing  fly  (Fig.  15).  These 
were  present  in  most  of  the  vineyards,  and  were  frequently  seen  feed- 
ing on  the  nymphs  of  the  hoppers,  but  their  number  was  not  large 
enough  to  have  any  appreciable  effect  whatever  in  reducing  the  abund- 
ance of  the  grape  leaf-hoppers.  Ladybird  beetles  and  their  larvae 
were  also  seen  to  feed  upon  the  nymphs,  but  they  did  not  occur  in 


Bulletin  198.  THE  GRAPE  LEAF-HOPPER.  203 

large  numbers.  Certain  spiders  which  make  their  webs  at  the  crown 
of  the  vine  seem  to  depend  for  food  very  largely  on  the  adult  hoppers 
that  are  caught  in  their  webs.  Ants  were  occasionally  seen  carrying 
away  young  nymphs  in  their  jaws.  The  ants  were  not  long  in  dis- 
covering our  supply  of  nymphs  in  the  laboratory,  which  was  on  the 
second  story  of  a  building,  and  soon  established  a  regular  line  of 
march,  where  they  could  be  seen  carrying  away  nymphs  to  their  nest 
in  the  ground  below.  A  small  red  mite  was  occasionally  found  on  the 
hoppers  at  Madera,  but  we  do  not  know  that  the  hoppers  were  actually 
killed  by  this  parasite. 

Fungous. — It  is  said  that  a  fungus  belonging  to  the  genus  Epusa 
destroyed  the  hoppers  in  Connecticut  in  1890. x  We  saw  no  evidence 
of  fungous  disease  during  the  past  two  years.  Neither  was  there  any 
great  mortality  of  hoppers  observed,  except  in  the  egg  stage  mentioned 
in  another  place,  and  in  this  case  it  seemed  to  be  due  to  the  infertility 
of  the  eggs  rather  than  an  attack  of  fungous  disease.  Since,  however, 
these  insects  occur  in  large  numbers  and  are  closely  associated,  once 
a  fungous  disease  gets  a  foothold,  large  numbers  are  likely  to  be 
destroyed. 

MECHANICAL   CONTROL. 

Blowers  and  Suction. — On  account  of  the  habit  of  the  hoppers  of 
flying  about  in  the  vicinity  of  the  vine  when  disturbed,  it  was  thought 
that  there  might  be  a  possibility  of  drawing  them  into  a  machine  by 
means  of  suction.  A  suction  machine  was  designed  and  is  said  to 
have  worked  successfully  in  capturing  the  Rocky  Mountain  locust  in 
1874  and  1876  when  the  notable  outbreaks  of  these  insects  occurred. 
This  principle  of  suction  is  also  used  in  sawmills  for  carrying  away  the 
sawdust. 

We  started  out  on  this  problem  by  experimenting  with  a  ventilating 
fan  run  by  a  gasoline  engine.  It  was  possible  to  draw  in  good  sized 
pieces  of  paper  and  other  objects  heavier  than  small  insects,  but  the 
distance  through  which  the  suction  worked  with  sufficient  force  was 
too  short  to  be  of  any  practical  use  against  the  hoppers.  In  order  that 
such  a  machine  may  work  successfully  it  would  be  necessary  to  draw  in 
the  insects  for  a  distance  of  at  least  three  or  four  feet.  This  might 
be  accomplished  with  a  very  much  larger  fan,  but  this  would  involve 
the  use  of  heavy  machinery  that  would  be  unwieldy  for  use  in  a 
vineyard,  so  that  we  abandoned  the  idea  of  control  by  suction  as  im- 
practicable. 

With  suction  the  air  is  drawn  in  with  about  equal  force  in  all 
directions  from  the  end  of  the  tube,  so  that  there  is  not  much  force  at 


1  Thaxter,  R.,  Conn.  Sta.  Rept.,  1890. 


204  UNIVERSITY   OF  CALIFORNIA EXPERIMENT   STATION. 

any  particular  point ;  but  the  air  is  blown  out  of  the  machine  in  a  very 
definite  column  and  with  much  force.  With  our  experimental  fan, 
objects  that  could  be  drawn  in  only  when  within  a  range  of  a  few 
inches,  could  be  blown  out  many  feet.  This  induced  us  to  try  blowing 
the  hoppers  into  a  funnel-shaped  receptacle.  For  this  purpose  a  large 
blacksmith's  rotary  bellows  was  used,  with  a  large  galvanized  iron 
funnel  three  or  four  feet  in  diameter  for  the  receptacle.  The  black- 
smith's bellows  did  not  produce  an  air  current  of  sufficient  diameter; 
for  this  to  work  successfully  the  diameter  of  the  current  of  air 
should  be  at  least  three  or  four  feet,  and  this  again  would  require 
bulky  machinery.  The  hoppers  also  held  on  very  tenaciously  to  the 
opposite  side  of  the  leaves  when  the  air  current  was  turned  on  them, 
and  thus  it  was  impossible  to  get  them  all  off  the  vine.  While  this 
method  of  fighting  the  hoppers  gave  more  promise  of  working  success- 
fully than  the  suction  method,  it  would  necessitate  the  use  of  rather 
expensive  and  cumbersome  machinery  that  would  not  appeal  to  the 
practical  vineyardist. 

Torches. — On  account  of  the  difficulty  of  killing  adult  hoppers  with 
any  spray  while  they  are  in  the  air,  we  tried  the  torch  as  a  means  of 
overcoming  this  difficulty.  The  torch,  which  was  tried,  consisted  of 
burning  the  kerosene  as  it  left  an  ordinary  spray  nozzle  which  would 
throw  a  very  fine  mist  spray.  This  was  tried  during  the  dormant 
season  on  the  hoppers  as  they  would  fly  up  from  the  vegetation  growing 
in  the  vineyards.  Even  with  this  many  hoppers  would  escape  around 
the  edges  of  the  flame,  and  this,  together  with  danger  of  scorching  the 
vine  when  in  foliage,  led  us  to  put  this  method  in  the  negative  list  of 
remedies. 

Dry  Powders. — It  has  been  very  positively  maintained  by  certain 
growers  that  they  could  kill  the  nymphs  of  the  vine  hopper  very 
successfully  by  the  use  of  air-slaked  lime.  In  order  to  determine  this 
we  made  a  number  of  experiments  by  keeping  nymphs  in  all  stages 
in  a  vial  and  thoroughly  dusting  them  and  filling  the  air  in  the  vial 
with  lime,  but  many  did  not  appear  to  be  inconvenienced  by  this 
treatment.  This  method  was  carried  out  on  a  practical  scale  by  thor- 
oughly dusting  a  row  of  vines  through  a  vineyard  by  means  of  the 
French  vermorel  machine  used  in  applying  sulfur  for  the  Oidium 
(Fig.  16).  The  air-slaked  lime  had  no  effect  whatever,  so  far  as  could 
be  observed,  on  the  number  of  nymphs. 

Pyrethrum  was  used  with  better  success  in  the  laboratory  experiments 
where  the  hoppers  were  confined,  but  the  results  in  the  vineyard  were 
not  at  all  satisfactory  in  controlling  the  nymphs.  The  expense,  more- 
over, of  pyrethrum  if  used  on  such  a  large  scale  would  be  too  great 
to  make  this  a  practical  remedy. 


Bulletin  J98.  THe  GRAPE  LEAF-HOPPER.  205 

The  idea  that  prevails  with  some,  that  sulfur  is  of  use  in  killing  the 
hoppers,  is  not  borne  out  by  facts.  Hoppers,  in  all  stages,  confined  in 
our  breeding  cages  in  the  vineyard,  thrived  well  in  spite  of  the  fact 
that  large  amounts  of  sulfur  were  blown  into  and  held  in  the  cages 
during  the  frequent  sulfurings  for  Oidium. 

Sticky  Shields. — Sticky  shields  have  been  used  to  some  extent  in 
fighting  the   grape  leaf-hopper,   but   a  large  number   escape   by  this 


Fig.  16.     Applying  air-slaked  lime  for  the  nymphs  of  the  hopper  by  means  of  the 
French  vermorel  machine. 

method  so  that  their  use  is  not  thoroughly  satisfactory.  A  sticky  shield 
held  on  .the  leeward  side  of  the  vine  and  the  hoppers  jarred  off  will 
catch  many,  but  a  large  number  will  not  strike  the  shield.  A  three- 
sided  box  for  our  California  vines  works  best,  but  even  here  many  will 
drop  to  the  ground  or  fly  out  on  the  open  sides.  In  the  New  York 
vineyards,  two  men  each  carrying  light  sticky  shields  three  or  four 
feet  high  and  seven  or  eight  feet  long  on  opposite  sides  of  trellised 
vines,  has  been  found  to  be  a  fairly  successful  method  of  capturing 
the  hoppers.  Probably  the  best  sticky  material  for  use  on  the  shields 
in  this  State  is  the  ordinary  crude  oil. 
3— Bul.  198 


206 


UNIVERSITY   OF   CALIFORNIA EXPERIMENT   STATION. 


Fumigation. — A  good  many  experiments  were  carried  on  with  a 
view  of  determining  the  feasibility  of  fumigation  as  a  means  of  con- 
trolling the  vine  hopper.  The  vines  were  enclosed  either  in  canvas 
tents,  or  a  galvanized  iron  tank  or  drum  inverted  over  the  vine,  or  a 
square  box  made  of  building  paper  (Fig.  17).  In  most  of  the  experi- 
ments carried  on  the  tank  or  box  was  used,  since  the  air  capacity  did 
not  vary  in  these  as  was  the  case  with  the  loose  canvas  tents,  and  the 
dosage  could  be  accurately  calculated. 

One  gram  of  cyanide  of  potassium  to  thirty  cubic  feet  of  space  was 


"~ • — 

**■ """~                                                  ^*djB|gAk<Jfctall 

h* 

mB^KL 

F^^yr- 

-' 

^ A  v 

':T 

£w  " 

- 

wk 

Fig.   17. 


Fumigating  box  made  of  building  paper,   used  in   the  experiments  on 
fumigation. 


found  to  kill  the  hoppers  in  from  five  to  ten  minutes.  In  some  cases 
with  this  dose,  however,  a  few  of  the  most  tender  leaves  would  be 
slightly  burned.  The  work  was  done,  however,  during  the  day  time, 
when  the  vine  is  more  active  and  more  susceptible  to  the  gas  than 
at  night.  Because  of  the  short  exposure  necessary  to  kill  the  hoppers 
a  few  tents  would  be  sufficient  to  keep  a  crew  of  fumigators  busy,  so 
that  the  initial  expense  of  apparatus  need  not  be  very  great.  The  dose 
necessary  for  each  vine  is  also  small,  so  that  there  is  not  a  large  expense 
of  chemicals.  The  moving  of  the  tents  from  vine  to  vine  and  the 
weighing  and  charging  of  the  chemicals,  however,  require  much  time 


Bulletin  198. 


THE  GRAPE  LEAF-HOPI'EK. 


207 


and  labor.  The  accurate  weighing  of  such  small  quantities  of  cyanide 
and  the  liability  of  injuring  the  vine  or  not  killing  the  insects,  if  this 
is  not  carefully  done,  make  the  method  too  complicated  for  the 
practical  vineyardists,  besides  being  more  expensive  than  other  methods 
of  control  discussed  farther  on. 

Some  experiments  were  tried  by  a  vineyardist  near  Lodi  with  burning 
sulfur  and  liberating  the  gas  in  a  drum  enclosing  the  vine,  as  shown  in 
figure  18.  A  fire  was  made  in  a  small  cylinder  on  the  side  of  the  drum 
and  sulfur  blown  over  this  by  means  of  an  ordinary  sulfur  bellows, 


Fig.  18.  An  apparatus  for  fumigating  with  the  fumes  of  sulfur,  designed 
'by  a  vineyardist  at  Lodi.  The  tent  in  the  background  is  for  hydro- 
cyanic acid  gas. 


thus  converting  the  sulfur  into  a  gas  which  was  conducted  through  a 
tube  entering  the  drum  near  the  bottom.  It  was  difficult  to  regulate 
the  amount  of  gas  with  this  apparatus,  so  that  the  vines  generally  were 
badly  scorched.  Some  modification  of  this  apparatus  might  be  made 
to  work  successfully;  but  sulfur  fumes  S02,  at  least  when  used  alone, 
is  not,  apparently,  a  good  insecticide,  and  on  the  other  hand,  plants  are 
very  susceptible  to  injury  by  this  gas.  There  is,  therefore,  a  very 
small  margin,  if  any,  between  a  dose  that  will  kill  the  insects  and  not 
injure  the  plant,  A  grower  at  Madera  thought  he  could  kill  the 
hoppers  by  burning  sulfur  between  the  vines.     A  handful  or  two  of 


208  UNIVERSITY   OF  CALIFORNIA EXPERIMENT  STATION. 

sulfur  on  a  piece  of  burlap  sacking  was  placed  between  every  four 
vines  over  about  one  quarter  of  an  acre,  and  the  sulfur  burned.  The 
hoppers  apparently  suffered  no  discomfiture,  but  the  foliage  on  the 
windward  side  of  the  vines  was  badly  burned. 

Sprays  and  Washes. — Various  kinds  of  sprays  and  washes  were 
tried  for  killing  the  adult  hoppers  in  the  spring,  and  also  during  the 
winter  while  they  were  still  on  their  winter  food-plants.  None  of 
these  were  successful  because  of  the  activity  of  the  hoppers,  for  it  was 
impossible  to  drench  those  in  the  air  thoroughly  enough  to  kill  them. 


Fig.  19.     Spraying  for  the  nymphs. 

Pure  kerosene  was  used  while  they  were  still  on  the  vegetation  in 
winter,  and  even  with  this  strong  material  probably  the  larger  per  cent 
escaped  on  account  of  their  activity.  They  could,  however,  be  quite 
readily  killed  if  they  were  against  something,  as  the  ground  or  a  leaf, 
where  the  spray  would  wet  them  thoroughly. 

Spraying  for  the  nymphs,  however,  is  a  different  problem,  and  it 
is  practical  to  get  a  very  large  per  cent  of  them  by  this  method.  The 
nymphs  are  all  on  the  underside  of  the  leaves  and  they  are  not  capable 
of  flying  or  jumping,  so  that  it  is  possible  to  hit  them  with  a  spray. 
The  sprays  which  gave  the  best  results  were  the  whale  oil  soap  solution 
and  the  resin  spray, — the  soap  solution  being  probably  a  little  the  better. 


Bulletin  198. 


THE  GRAPE  LEAF-HOPPER. 


209 


One  pound  of  soap  was  used  to  fifteen  gallons  of  water.  In  the  case 
of  the  resin  one  pound  was  used  with  fifteen  gallons  of  water  and  enough 
lye  or  potash  to  completely  dissolve  the  resin.  This  is  at  the  rate  of 
one  pound  of  lye  to  about  eight  pounds  of  resin. 

The  time  to  spray  for  the  nymphs  is  when  they  first  reach  their 
maximum  numbers  in  the  spring,  just  before  the  first  of  them  change 
into  the  adult  winged  hoppers.  This  was  during  the  last  of  May  and 
the  first  of  June  during  the  past  two  years  at  Lodi. 

The  spray  should  be  applied  from  below  and  the  under  side  of 
every  leaf  thoroughly  wetted  with  the  solution,  since  the  spray  will 
kill  no  more  nymphs  than  it  hits.     This  is  not  very  difficult  to  do  in 


Fig.  20.  An  apparatus  designed  by  a  vineyardist  at  Madera  for  use  against 
both  the  leaf -hopper  and  grasshoppers.  The  trough  at  the  bottom  con- 
tains crude  oil,  into  which  the  hoppers  are  supposed  to  fall  upon  hitting 
the  upright  screen. 

May  or  early  June,  while  the  shoots  are  still  comparatively  short.  The 
best  type  of  nozzle  to  use  is  the  cyclone,  with  the  spray  emerging  at 
right  angles  with  the  long  axis  of  the  rod,  shown  in  figure  19.  This 
will  allow  the  operator  to  poke  the  rod  anywhere  among  the  vines  with- 
out its  being  caught. 

The  spray  is  intended  to  kill  the  nymphs  only.  There  are  adults 
always  present  which  will  escape,  and  the  spray  will  not  prevent  what- 
ever eggs  may  be  present  from  hatching  later.  In  bad  cases  of  vine 
hopper  injury,  however,  it  will  pay  well  to  do  this  spraying  for  the 
nymphs,  if  the  screen  method,  described  below,  has  not  been  used  or 
the  work  not  effectually  done. 


210 


UNIVERSITY    OF   CALIFORNIA EXPERIMENT   STATION 


Screens  or  Cages. — In  our  work  of  spraying  for  the  adults  it  was 
soon  determined  that,  if  a  spray  was  to  be  used  successfully,  the 
active  hoppers  must  be  confined  within  certain  limits  in  order  to  give 
time  to  hit  them  thoroughly  with  the  spray.  The  screen  cage  shown  in 
Fig.  21  was  developed  as  a  result  of  this,  it  being  intended  to  apply 
the  spray  from  the  open  side  through  a  hole  in  a  canvas  curtain  which 
eould  be  dropped  down  as  the  cage  was  pushed  onto  the  vine.     This 


Fig.  21.     A  screen  cage  used  to  capture  the  grape  leaf-hopper. 


was  found  to  work  quite  satisfactorily.  It  was  noticed,  however, 
that  when  the  base  of  the  V-shaped  opening  on  the  bottom  of  the  cage 
struck  the  vine  most  of  the  hoppers  were  jarred  off.  This  suggested  the 
use  of  a  sticky  material  on  the  sides  and  bottom  of  the  cage  and  jarring 
them  on  to  this,  and  thus  dispensing  with  the  spray. 

This  method  of  capturing  the  adult  hoppers  by  means  of  the  screen 
cage  in  the  early  spring  proved  to  be  the  most  successful  of  all  the 
means  of  control  tried  during  the  season. 

Thf  screen    cage   is  made   by  tacking   a  double  layer  of  ordinary 


Bulletin  198. 


THE  GRAPE  LEAF-HOPPER. 


211 


more 

is    necessary 


galvanized  mosquito  wire-netting  over  a  square  frame  of  wood  or 
laths  or  other  light  material.  A  single  covering  of  mosquito  netting 
will  allow  some  hoppers  to  escape  through  the  mesh.  If  it  is  obtainable, 
a  20-mesh  screen  would  be  preferable.  Ordinary  galvanized  mos- 
quito wire-netting,  however,  can  be  obtained  almost  anywhere,  and 
two  layers  of  it  work  very  satisfactorily.  The  bottom  of  the  cage 
consists  of  a  shallow  tray.  This  is  made  by  turning  up  about  an  inch 
or  an  inch  and  a  half  of  the  edges  of  a  sheet  of  light  galvanized  iron. 
There  are  two  grades  of  this  iron,  and  the  heavier  grade  adds  much 
weight  than 
One 
side  of  the  box  is 
kept  open  and  there 
is  a  V-shaped  open- 
ing (Fig.  22)  in  the 
tray  at  the  bottom 
which  permits  the 
cage  to  be  pushed 
on  to  the  vine.  At 
the  same  time  that 
the  cage  is  swung 
into  position  the  vine 
is  bumped  by  the 
base  of  the  opening, 
which  is  padded 
with  leather,  thus 
jarring  the  hoppers 
off.  The  sides  and 
bottom  of  the  cage, 
having  been  pre- 
viously smeared 
with  crude  oil,  catch 
all  the  hoppers  that 

fall  on  to  them.  The  cage  should  be  operated  with  the  open  side  facing 
the  direction  from  which  the  wind  is  blowing.  If  there  is  a  breeze 
blowing,  very  few  will  escape  on  the  open  side.  However,  if  there  is 
no  breeze,  and  the  hoppers  are  especially  active,  a  canvas  curtain 
fastened  on  the  front  of  the  cage  at  the  top  can  be  very  readily  dropped 
down  as  the  cage  comes  into  position,  thus  shutting  off  all  possibility 
of  escape. 

The  bottom  of  the  cage  is  a  very  essential  feature,  since  most  of  the 
hoppers  drop  to  the  bottom  at  the  back  of  the  cage  or  are  caught  within 
a  foot  or  two  from  the  bottom  on  the  sides.  To  prevent  any  escaping 
by  dropping  down  through  the  opening. in  front  of  the  vine  this  may 


Fi| 


The  hopper  cage  with  the  V-shaped  opening  at 
the    bottom    covered    with    canvas. 


212  UNIVERSITY  OF  CALIFORNIA EXPERIMENT   STATION. 

be  covered  with  canvas  as  shown  in  figure  22.  Two  pieces  of  canvas 
meeting  in  the  center  are  tacked  on  the  sides  of  the  opening.  Pieces 
of  rubber  tubing  extending  transversely  are  sewed  on  the  canvas  and 
their  ends  securely  tacked  down  at  the  sides,  leaving  them  otherwise 
free,  excepting  as  they  are  fastened  in  the  canvas.  As  the  cage  is 
pushed  on  to  the  vine  the  canvas  and  the  free  ends  of  the  rubber  give 


Fig.  23.  A  photograph  of  the  interior  of  the  cage  shown  in  Fig.  21,  after 
15  minutes  use  where  hoppers  were  very  abundant.  The  white  specks  at 
the  back  each  represents  a  hopper,  stuck  in  the  oil  with  which  the  screen 
has  been  smeared.  A  portion  of  the  tray  at  the  bottom,  which  is  outside 
the  shadow  on  the  left,   shows  a  solid  surface  of  hoppers. 

way,  but  immediately  spring  back  into  position  again  on  account  of 
the  flexibility  of  the  rubber  tubing.  This  canvas  may  be  covered  with 
oil,  and  thus  the  bottom  is  completely  covered. 

The  advantage  of  the  screen  is  that  it  does  not  shut  off  the  light 
and  also  allows  the  wind  to  blow  through  so  that  the  great  majority  of 
the  hoppers  will  go  downward  and  toward  the  leeward  side  of  the  vine. 
A  cage  built  of  canvas  was  tried,  but  proved  unsuccessful   because 


Bulletin  198.  THe  GRAPE  LEAF-HOPPER.  213 

most  of  the  hoppers  came  out  on  the  open  side  toward  the  light,  and 
it  was  with  difficulty  that  they  could  be  caught  on  the  black  oiled 
canvas.  The  canvas  also  absorbs  more  of  the  oil  than  the  screen  and 
makes  a  drier  surface  for  the  hoppers  to  light  upon,  thus  failing  to 
hold  them  as  well  as  the  free  oil  on  the  wire  of  the  screen. 

Kerosene  may  be  used  on  the  screen  as  well  as  crude  oil,  but  it 
evaporates  more  rapidly  and  more  frequent  applications  are  necessary. 
For  a  fine  mesh  screen,  however,  the  kerosene  works  very  well,  since 
it  does  not  darken  the  sides  so  much  as  the  black  crude  oil. 

The  time  to  use  this  screen  cage  is  in  the  early  spring  when  the 
shoots  of  the  vine  are  not  more  than  four  or  five  inches  long.  At  this 
time  all  the  hoppers  have  left  their  winter  food  plants  and  have  begun 
to  feed  upon  the  vines,  and  none  have  yet  laid  eggs.  This  method, 
therefore,  captures  them  at  a  critical  time  before  they  have  begun  to 
breed,  and  thus  greatly  reduces  the  numbers  of  the  succeeding  gen- 
erations. 

The  work  may  also  be  done  more  easily  and  effectively  at  this  time, 
since  there  is  not  the  excessive  foliage  that  appears  as  the  season 
advances.  The  size  of  the  vines  to  be  treated  will  determine  the  size 
of  the  cage.  Ordinarily,  the  cage  need  be  but  very  little  larger  than 
the  diameter  of  the  vines  after  pruning.  In  one  young  vineyard,  two 
years  old,  the  hoppers  were  kept  down  successfully  by  a  small  cage 
about  one  foot  square,  which  was  easily  handled  by  one  man.  With  the 
larger  cages  three  feet  square,  handles  are  attached  to  each  side  and 
the  cage  manipulated  by  two  men.  One  of  these  cages  with  two  men 
will  go  over  four  or  five  acres  a  day.  There  is  practically  no  expense 
for  materials  and  the  time  of  the  men  is  the  chief  outlay. 

If  this  screen  cage  is  conscientiously  used  it  will  capture  from  85% 
to  95%  of  the  hoppers,  and  at  a  time  in  the  life-history  of  the  insect 
when  for  each  hopper  taken  it  means  a  hundred  or  so  less  later  in  the 
summer. 

This  method  of  capturing  the  hoppers  with  the  screen  cage  was 
developed  for  vines  that  are  headed  some  little  distance  above  the 
surface  of  the  ground.  There  are  many  vineyards  in  the  State,  however, 
that  have  not  been  so  pruned.  Some  are  headed  directly  at  the  surface, 
and  in  some  even  the  canes  come  out  from  the  stump  beneath  the 
surface,  and  a  cone-shaped  area  is  scooped  away  to  make  room  for  the 
growth  of  the  canes.  This  form,  in  some  cases,  is  given  to  the  vine 
by  frost;  but  where  the  pruning  is  responsible,  it  is  generally  considered 
now  to  be  a  bad  system. 

If  the  cage  is  to  be  used  on  such  vines,  it  must  be  done  with  some 
modification  of  the  bottom  or  the  bottom  dispensed  with  entirely,  though 
this  is  an  important  part  of  the  apparatus. 


214  UNIVERSITY   OF  CALIFORNIA EXPERIMENT   STATION. 

In  the  case  of  staked  vines  it  is  possible  to  work  this  cage  if  the 
top  is  left  off,  or  enough  of  the  top  so  as  not  to  interfere  with  the 
stake.  An  opening  may  be  left  in  the  top  similar  to  the  V-shaped 
opening  at  the  bottom.  A  staked  vineyard  was  gone  over  with  this 
modified  cage  and  practically  no  hoppers  escaped  through  the  opening 
at  the  top.  Such  an  apparatus  can  not  be  used  at  all,  of  course,  on 
trellised  vines.  For  trellised  vines  we  would  suggest  the  use  of  sticky 
shields  as  are  used  in  New  York  vineyards,  excepting  that  the  canvas 
be  replaced  by  wire  screen  netting.  These  should  be  three  or  four  feet 
high  and  seven  or  eight  feet  long,  and  two  of  them  operated  together 
on  opposite  sides  of  the  trellis. 

FARM  PRACTICES. 

Plowing. — Plowing  is  sometimes  done  by  California  vineyardists 
during  the  winter  season  for  the  purpose  of  destroying  the  grape  leaf- 
hoppers.  This  is  partly  based  upon  the  supposition  that  the  eggs 
may  be  in  the  leaves  or  in  the  ground,  or  that  the  adult  hoppers  are 
in  some  way  killed  in  the  operation.  So  far  as  having  a  direct  effect 
in  destroying  the  hoppers  is  concerned,  plowing  is  of  little  avail.  The 
only  ones  that  will  be  killed  are  a  few  that  may  not  be  disturbed  from 
their  resting  places  among  the  leaves,  or  otherwise  accidentally  buried 
by  the  plow.  During  the  cold  or  rainy  days  there  may  be  a  few  thus 
turned  under,  but  ordinarily  they  are  active  enough  to  escape  readily 
before  the  plow. 

Plowing,  however,  may  have  an  indirect  effect  on  the  hoppers  by 
depriving  them  of  food,  or  of  suitable  sheltering  places  during  un- 
favorable weather  conditions,  and  if  this  practice  is  generally  carried 
out  in  a  neighborhood  it  will  no  doubt  result  in  reducing  the  numbers 
somewhat.  However,  a  field  may  be  free  from  hoppers  during  the 
winter,  but  this  is  not  necessarily  an  indication  of  freedom  from  spring 
infestation.  The  insects  are  more  generally  distributed  in  the  winter 
season,  but  the  bulk  of  them  will  usually  be  found  in  the  vineyard,  or 
on  the  vegetation  of  the  borders  immediately  surrounding  it.  They 
may  come  in,  therefore,  from  vineyards  closely  adjoining,  so  that 
plowing  a  single  vineyard  may  be  of  little  help.  When  the  plowing  is 
done  in  a  single  vineyard  or  over  a  small  area  it  is  likely  to  result 
simply  in  driving  them  into  other  fields,  where  there  is  a  better  food 
supply.  Once  in  these  other  situations  they  may,  or  may  not,  come 
back  into  the  vineyard  where  they  were  originally. 

Sheeping. — Some  growers  turn  sheep  into  the  vineyard  soon  after 
the  crop  is  harvested  and  allow  them  to  eat  off  the  leaves  of  the  vines. 
This  should  not  be  done  until  the  leaves  have  completed  their  growth 


Bulletin  198.  THE  GRAPE  LEAF-HOPPER.  215 

and  are  about  ready  to  fall  naturally.  The  chief  result  of  this  practice 
is  to  drive  the  hoppers  elsewhere  for  food.  In  the  late  fall  the  adult 
hoppers  are  still  feeding  on  the  vine  foliage,  and  there  they  continue  to 
feed  until  the  leaves  lose  their  succulent  material  and  dry  up.  When 
sheep  are  turned  in  among  the  vines  and  the  foliage  eaten  off,  the 
hoppers  will  either  go  to  an  adjoining  vineyard  that  is  still  in  foliage, 
or  simply  begin  to  feed  a  little  earlier  on  their  wide  range  of  winter 
food  plants  which  may  be  growing  in  the  vineyard  or  vicinity.  The 
destruction  of  the  leaves,  however,  does  away  with  the  sheltering  places 
that  would  be  formed  by  the  leaves  accumulating  in  bunches  by  the 
wind ;  and  a  clean  vineyard  is  always  freer  from  hoppers  in  the  winter 
season  than  one  where  there  is  an  abundance  of  leaves  or  of  groAving 
vegetation.  But  there  is  nothing  to  protect  such  a  vineyard  from  a 
possible  infestation  in  the  spring  from  the  adjoining  vineyards. 

Plowing  and  sheeping,  then,  result  chiefly  in  partially  destroying  the 
food  supply  over,  a  limited  area,  and  of  doing  away  with  possible 
hibernating  places  in  the  bunches  of  leaves  that  would  otherwise 
accumulate.  The  usefulness  of  such  practices  will  depend  largely  on 
how  generally  they  are  carried  out  in  a  neighborhood,  and  at  best  can 
be  counted  on  simply  to  reduce  the  number  of  hoppers,  which,  generally, 
is  not  likely  to  be  at  a  point  of  effective  control. 


SUMMARY. 

The  grape  leaf-hopper  is  one  of  the  most  important  insect  pests  of 
the  vine  in  California,  as  may  be  seen  by  the  most  casual  observer  in 
the  large  amount  of  foliage  that  dries  up  prematurely  on  the  vines  in 
many  sections  of  the  State  each  year. 

Life  History. — The  hoppers  pass  the  winter  as  adult  insects  on  a  wide 
range  of  food  plants  that  may  be  growing  in  the  vineyard  or  vicinity. 

They  attack  the  vine  as  soon  as  the  foliage  appears,  and  here  they 
remain  until  the  leaves  fall  in  the  autumn. 

One  month  after  they  begin  feeding  on  the  vine,  the  overwintering 
hoppers  begin  egg  laying,  which  is  continued  over  a  period  of  a  month 
or  two,  after  which  they  die.  The  hoppers  of  the  spring,  brood  arising 
from  eggs  laid  in  May,  become  full  grown  in  three  weeks,  begin  egg 
laying  two  or  three  weeks  later,  and  die  off  in  August  or  September, 
making  the  life  of  this  spring  brood  approximately  three  or  four  months. 
Hoppers  arising  from  eggs  laid  by  the  spring  brood  in  June  and  later, 
remain  on  the  vine  until  the  leaves  fall  in  autumn.  They  then  take  to 
whatever  succulent  vegetation  may  be  present  in  the  neighborhood, 
where  they  live  over  winter  and  attack  the  vines  again  in  the  following 


216  UNIVERSITY  OF  CALIFORNIA — EXPERIMENT  STATION. 

spring.  These  begin  depositing  eggs  a  month  after  the  leaves  appear 
on  the  vine,  and  die  off  in  midsummer,  making  the  length  of  this  life 
cycle  approximately  one  year  in  the  central  valleys  of  California. 

Control. — The  most  satisfactory  control  method  tried  during  the  past 
two  years  was  the  use  of  the  screen  cage.  This  was  found  to  capture 
about  85%  to  95%  of  the  adult  hoppers  at  a  time  in  the  spring  before 
any  eggs  are  deposited. 

Spraying  for  the  nymphs  about  June  1st,  or  just  before  the  spring 
brood  becomes  mature,  will  kill  a  satisfactory  percentage  of  the  nymphs 
or  young,  but  will  not  kill  many  adults,  or  prevent  eggs,  which  are 
present  at  this  time,  from  hatching  later.  If  the  cage  method  has  not 
been  used,  or  satisfactorily  operated,  spraying  for  the  nymphs  will  very 
materially  aid  in  reducing  the  numbers  of  the  spring  generation. 

Plowing  or  other  farm  practices  can  not  be  relied  upon,  but  when 
such  measures  are  generally  practiced  throughout  a  neighborhood,  they 
may  aid  in  reducing  the  numbers  somewhat. 


LITERATURE.  217 


LITERATURE. 

1825.  Say,  Thomas.     Jour.   Acad.  Nat.   Sci..  Phil.,  iv,  327. 

1828.  Fessenden.     New  Am.  Gard.,  Bost.,  299. 

1831.  Harris,  T.  W.     Encycl.  Amer.,  viii,  43, 

1841.  Harris,  T.  W.     Insects  Inj.  to  Veg.,  Flint  Ed.,  22S. 

1843.  Allen,  Pract.  Treatise  on  the  Grape  Vine,  132. 

1848.  Downing's   Horticulturist,   iii,    28. 

1854.  Glover,  Towend.     Rpt.  U.  S.  Agr.,  77-78. 

1856.  Fitch,  A.    3rd  Rpt.  on  Insects  of  N.  Y.,  391. 

1861-2.  Fitch,  A.     7th  Rpt.  on  Insects  of  ,N.  Y. 

1864.  Walsh,  B.   D.     Proc.  Boston  Soc.   Nat.   Hist,  ix,  317-318. 

1867.  Walsh,  B.  D.  Pract.  Ent,  ii,  49-52. 

1868.  Bethune,  C.  J.  S.     Can.  Farmer,  v,  113-114. 

1868.  Kirkpatrick,  J.     Ohio  Farm.,  iii,  3. 

1869.  Walsh,  B.  D.  and  Riley,  C.  V.     Am.  Ent.,  i,  227. 

1870.  Saunders,  W.     Rpt.  Fruit  Grow.  Assoc,  Ont,  94-117. 

1871.  Glover,  T.     Monthly  Rpt.  U.  S.  D.  A.,  Nov.  and  Dec,  477-480. 
1871.  Saunders,  W.     Rpt.  Ent.   Soc,  Ont,  17-21. 

1871.  Glover,  T.     Rpt.  U.  S.  Com.  Agr.,  69-88. 

1873.  Riley,  C.  V.     Trans.  111.  St.  Hort.   Soc,  vii.  138. 

1875.  Packard,  A.   S.     Rpt.  U.   S.   Geol.   Sur.,  1875-77-78. 

1875.  Cook,  A.  J.     13th  Ann.  Rpt  St.  Bd.  Agr.,  Mich. 

1876.  Glover,  T.     Rpt  U.  S.  D.  A.,  p.  32. 

1877.  Packard,  A.  S.     Am.  Nat,  ii,  786. 

1878.  Perkins,  G.  H.     5th  Rpt.  Ver.  Bd.  Agr.,  250-286. 
1880.  Riley,  C.  V.     Amer.  Ent,  i,  182. 

1883.  Devereaux,  W.  L.     Rural  New  Yorker,  vol.  47,  p.  474. 

1883.  Saunders,  W.     Ins.  Inj.  to  Fruits,  286. 

1884.  Uhler,  P.     Stand.  Nat.  Hist,  ii,  246. 

1885.  Lintner,  J.  A.     33d  Ann.  Rpt.  Mass.  Bd.  Agr.,  165-196. 

1887.  Lintner,  J.  A.     Cult,  and  Count.  Gent,  Iii,  493. 

1888.  Lintner,  J.   A.     Vineyardist,  ii.  113. 

1888.  Fernald,  C.  H.     Mass.  Hatch.  Exp.  Sta.  Bull.  2,  p.  3. 

1888.  Bethune,  C.  J.  S.     19th  Ann.  Rpt.  Ent.   Soc,  Ont,  63-74. 

1888.  Marvin,   D.   S.     Rural  New  Yorker,   Sept   576. 

1889.  Woodworth.  C.  W.     Psyche,  v.  213. 

1889.  Fernald,  C.  H.     Orange  Judd.  Farm.,  xviii,  May. 

1889.  Fernald,  C.  H.     Mass.  Hatch.  Exp.  Sta.  Rpt,  p.  21. 

1890.  Provancher.     Pet.  Fauna  Ent.  Can.,  iii,  298. 
1890.  Cassidy,  J.     Bull.  6,  Colo.  Exp.  Sta. 

1890.  Thaxter,   R.     Conn.    Sta.   Ann.   Rpt.   95-98. 

1890.  Blount,  A.  E.     Bull.  2,  N.  M.  Exp.  Sta.,  378-386. 

1890.  Gravestock,  J.     Proc   Colo.   Sta.  Hort.   and  Forest  Assoc. 

1891.  Gillette,  C.  P.     Bull.  15,  Colo.  Agr.   Exp.   Sta.   18. 
1891.  Fletcher,  J.     Can.  Cent.  Exp.  Farm.  Bull.,  xi.  May. 
1891.  Townsend,  C.  H.  T.     N.  M.  Exp.  Sta.  Bull.,  iii. 
1891.  Weed,  C.  M.     Ann.  Rpt  Columbus  Hort.  Soc,  166. 
1891.  Cockerell,  T.  D.  A.     N.  M.  Agr.  Exp.   Sta.  Rpt.  114. 

1891.  Lintner,  J.   A.     Country  Gentlemen,   Oct.,   815. 

1892.  Weed,  C.  M.     Insects  and  Insecticides. 
1892.  Townsend,  C.  H.  T.     N.  Mex.  Sta.  Bull.  5. 

1892.  Gillette,  C.  P.     Colo.  St.  Bd.  Hort..  230. 

1893.  Osborn,  H.     Trans.  Iowa  St.  Hort.  Soc.  262-264. 
1893.  Fletcher,   J.     Rpt.   Exp.   Farms.   Can.,   157-193. 

1893.  Fitch,  A.     Reprint  Lintners  9th  Rpt.   Ins.   N.   Y..   403. 

1893.  Webster,  F.  M.     Ann.  Rpt  Ohio  St.  Hort.  Soc.  63-76. 

1894.  Van  Duzee,  E.  P.     Trans.  Am.  Ent.  Soc,  xxi,  312. 

1894.  Gravestock,  J.     Proc.  Colo.  St.  Hort.  Assoc,  229-233. 

1895.  Gillette,  C.  P.     Colo.  Sta.  Bull.  15. 

1895.  Marlatt,  C.  L.     U.  S.  D.  A.  Yearbook,  385-404. 

1895.  Gillette,  C.  P.  and  Baker,  C.  F.     Colo.  Exp.  Sta.  Bull.  31,  p.  113. 

1895.  Comstock,  J.   H.     Manual   of  Insects.   154. 

1895.  Webster,  F.  M.     Ohio  Farm.,  Nov.  373. 
*1896.  Lugger,  O.     Minn.   Sta.  Bull.,  48. 
*1896.  Marlatt,  C.  L.     Am.  Nat.  Sept.  759. 

1896.  Slingerland,  M.  V.     Rural  New  Yorker,  17th  Oct.,  689. 

1896.  Smith,  J.   B.     Economic  Entom.,   148. 

1897.  Woodworth.   C.   W.     Cal.    Sta.   Bull.,   116. 
1897-8.  Clarke,  W.  T.    Ann.  Rpt.  Cal.  Sta. 

1900.  Gillette,  C.  P.     Ann.   Rpt  Colo.   Sta. 


218  LITERATURE STATION  PUBLICATIONS 

1901.  Felt,  E.  P.     Bull.  N.  Y.  St.  Mus.,  53. 

1901.  Slingerland,  M.  V.      Cornell  Exp.   Sta.  Bull.  215. 

1902.  Felt.  E.  P.     Proc.  14th  Ann.  Meet.  A.  E.  E.,  Bull.  37,  U.  S.  D.  A. 

1903.  Slingerland,  M.  V.     Rpt.  1903  Meet.  A.  A.  A.  S. 

1903.  Okla.  Sta.  Rpt.,  pp.  15-71. 

1904.  Smith.  J.  B.     N.  J.  Sta.  Rpt.  557-652. 

1907.  Quaintance,  A.  L.     Farm.  Bull.  284,  U.  S.  D.  A. 

1907.  Woodworth,  C.  W.     Insects  of  Cal.,  44. 

1908.  Quayle,  H.  J.     Jour.  Ec.  Ent,  v.  3,  no.  1. 


STATION  PUBLICATIONS  AVAILABLE  FOR  DISTRIBUTION 


REPORTS. 


1896.  Report   of    the    Viticultural    Work   during    the   seasons    1887-93,    with    data 

regarding  the  Vintages  of  1894-95. 

1897.  Resistant   Vines,    their    Selection,    Adaptation,    and   Grafting.      Appendix    to 

Viticultural  Report  for  1896. 

1898.  Partial  Report  of  Work  of  Agricultural   Experiment  Station   for  the  year* 

1895-96  and  1896-97. 
1900.     Report  of  the  Agricultural  Experiment  Station  for  the  year  1897-98. 

1902.  Report  of  the  Agricultural  Experiment  Station  for  1898-1901. 

1903.  Report  of  the  Agricultural  Experiment  Station  for  1901-1903. 

1904.  Twenty-second  Report  of  the  Agricultural  Experiment  Station  for  1903-1904. 

'      TECHNICAL  BULLETINS— ENTOMOLOGICAL  SERIES. 

Vol.  1,  No.  1 — Wing  Veins  of  Insects. 

No.  2 — Catalogue  of  the  Ephydridse. 

BULLETINS. 

Reprint.  Endurance  of  Drought  in  Soils  of  the  Arid  Region. 

No.  128.  Nature,  Value  and  Utilization  of  Alkali  Lands,  and  Tolerance  of  Alkali. 
(Revised  and  Reprint,  1905.) 

133.  Tolerance  of  Alkali  by  Various  Cultures. 

140.  Lands  of  the  Colorado  Delta  in  Salton  Basin,  and  Supplement. 

142.  Grasshoppers  in  California. 

147.  Culture  Work  of  the  Substations. 

149.  California  Sugar  Industry. 

150.  The  Value  of  Oak  Leaves  for  Forage. 

151.  Arsenical  Insecticides. 

152.  Fumigation  Dosage. 

153.  Spraying  with  Distillates. 

154.  Sulfur  Sprays  for  Red  Spider. 
156.  Fowl  Cholera. 

158.  California  Olive  Oil ;   its  Manufacture. 

159.  Contribution  to  the  Study  of  Fermentation. 

160.  The  Hop  Aphis. 

161.  Tuberculosis  in  Fowls.      (Reprint.) 

162.  Commercial  Fertilizers.     (Dec.  1,  1904.) 

163.  Pear  Scab. 

164.  Poultry  Feeding  and  Proprietary  Foods.     (Reprint.) 

165.  Asparagus  and  Asparagus  Rust  in  California. 

166.  Spraying  for  Scale  Insects. 

167.  Manufacture  of  Dry  Wines  in  Hot  Countries. 

168.  Observations  on  Some  Vine  Diseases  in  Sonoma  County. 

169.  Tolerance  of  the  Sugar  Beet  for  Alkali. 

170.  Studies  in  Grasshopper  Control. 

171.  Commercial  Fertilizers.      (June  30,  1905.) 

172.  Further  Experience  in  Asparagus  Rust  Control. 

174.  A  New  Wine-Cooling  Machine. 

175.  Tomato  Diseases  in  California. 

176.  Sugar  Beets  in  the  San  Joaquin  Valley. 

177.  A  New  Method  of  Making  Dry  Red  Wine. 

178.  Mosquito  Control. 


STATION  PUBLICATIONS. 


210 


No.  179.  Commercial  Fertilizers.      (June,  190(5.) 

180.  Resistant  Vineyards. 

181.  The  Selection  of  Seed- Wheat. 

182.  Analysis  of  Paris  Green  and  Lead  Arsenate.     Proposed  Insecticide  Law 

183.  The  California  Tussock-moth. 

184.  Report  of  the  Plant  Pathologist  to  July  1,  1906. 

185.  Report  of  Progress  in  Cereal  Investigations. 

186.  The  Oidium  of  the  Vine. 

187.  Commercial   Fertilizers.      (January,   1907.) 

188.  Lining  of  Ditches  and  Reservoirs  to  Prevent  Seepage  Losses. 

189.  Commercial  Fertilizers.     (June,  1907.) 

190.  The  Brown  Rot  of  the  Lemon. 

191.  California  Peach  Blight. 

192.  Insects  Injurious  to  the  Vine  in  California. 

193.  The  Best  Wine  Grapes  for  California ;   Pruning  Young  Vines ;    Pruning 

the  Sultanina. 

194.  Commercial  Fertilizers   (Dec.  1907). 

195.  The  Imported  Grape  Root- Worm. 

196.  Eucalyptus  in  California. 

197.  Grape  Culture  in  California  ;  Improved  Methods  of  Wine  Making  ;  Yeasts 

from  California  Grapes. 


CIRCULARS. 


No. 


1. 
2. 
3. 

4. 
5. 

7. 

9. 

10. 

11. 
12. 
13. 

15. 


16. 
17. 

18. 
19. 
21. 

22. 

23. 
24. 

25. 


Texas  Fever. 

Blackleg. 

Hog  Cholera. 

Anthrax. 

Contagious  Abortion  in  Cows. 

Remedies  for  Insects. 

Asparagus  Rust. 

Reading  Course  in  Economic 
Entomology.      (Revision.) 

Fumigation  Practice. 

Silk  Culture. 

The  Culture  of  the  Sugar  Beet 

Recent  Problems  in  Agriculture. 
What  a  University  Farm  is 
for. 

Notes  on  Seed-Wheat. 

Why  Agriculture  Should  be 
Taught  in  the  Public  Schools. 

Caterpillars  on  Oaks. 

Disinfection  of  Stables. 

The  Advancement  of  Agricul- 
tural Education. 

Defecation  of  Must  for  White 
Wine. 

Pure  Yeast  in  Wineries. 

Olive  Pickling. 

Suggestions  Regarding  Exam- 
ination of  Lands. 


No.  26. 


28. 


29. 


30. 
31. 


32. 
33. 

34. 


35. 


36. 


Selection  and  Preparation  of 
Vine  Cuttings. 

Marly  Subsoils  and  the  Chlo- 
rosis or  Yellowing  of  Citrus 
Trees. 

A  Preliminary  Progress  Report 
of  Cereal  Investigations, 
1905-07. 

Preliminary  Announcement  Con- 
cerning Instruction  in  Prac- 
tical Agriculture  upon  the 
University  Farm,  Davisville, 
California. 

White  Fly  in  California. 

The  Agricultural  College  and  Its 
Relationship  to  the  Scheme  of 
National   Education. 

White  Fly  Eradication. 

Packing  Prunes  in  Cans.  Cane 
Sugar  vs.  Beet  Sugar. 

California  State  Farmers'  In- 
stitute at  the  University 
Farm. 

Southern  California  Patholog- 
ical Laboratory  and  Citrus 
Experiment  Station. 

Analyses  of  Fertilizers  for  Con-, 
sumers. 


Copiea  may  he  had  on  application  to  Director  of  Experiment  Station,  Berkeley,  Cal. 


